(SOLVED) Would a low-latency kernel make a difference?

[amc252]

Hello everybody,

I have set up a minimal devuan system on a spare partition to play around with music.
If I play my midi keyboard with fluidsynth there is no noticeable latency, but if I play it with linuxsampler I can see a slight delay.
So, I have installed a second kernel, low-latency liquorix-6.0.0-10.1-amd64 to see if it would improve performance.
I could not see any significant improvement.
My laptop is a Toshiba Satellite with the following characteristics:

Code: Select all

 sudo lshw
                          

description: Notebook
product: Satellite C55-B (PSCMNU)
vendor: TOSHIBA
version: PSCMNU-01SNB1
serial: ZE091570P
width: 64 bits
capabilities: smbios-2.8 dmi-2.8 smp vsyscall32
configuration: boot=normal chassis=notebook family=* sku=PSCMNU uuid=05E5289C-7C4D-11E4-85C7-F0761C4DCFB0
  *-core
       description: Motherboard
       product: ZBWAA
       vendor: TOSHIBA
       physical id: 0
       version: 1.00
       serial: *
       slot: *
     *-firmware
          description: BIOS
          vendor: TOSHIBA
          physical id: 0
          version: 1.60
          date: 11/27/2014
          size: 64KiB
          capacity: 1MiB
          capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int14serial int17printer acpi usb biosbootspecification uefi
     *-memory
          description: System Memory
          physical id: e
          slot: System board or motherboard
          size: 4GiB
        *-bank:0
             description: DIMM DDR3 1333 MHz (0.8 ns)
             product: M471B5173DB0-YK0
             vendor: Samsung
             physical id: 0
             serial: 18219D3F
             slot: A1_DIMM0
             size: 4GiB
             width: 64 bits
             clock: 1333MHz (0.8ns)
        *-bank:1
             description: DIMM [empty]
             product: Array1_PartNumber1
             vendor: A1_Manufacturer1
             physical id: 1
             serial: A1_SerNum1
             slot: A1_DIMM1
     *-cache:0
          description: L1 cache
          physical id: 18
          slot: CPU Internal L1
          size: 112KiB
          capacity: 112KiB
          capabilities: internal write-back
          configuration: level=1
     *-cache:1
          description: L2 cache
          physical id: 19
          slot: CPU Internal L2
          size: 1MiB
          capacity: 1MiB
          capabilities: internal write-back unified
          configuration: level=2
     *-cpu
          description: CPU
          product: Intel(R) Celeron(R) CPU  N2840  @ 2.16GHz
          vendor: Intel Corp.
          physical id: 1a
          bus info: cpu@0
          version: Intel(R) Celeron(R) CPU N2840 @ 2.16GHz
          slot: SOCKET 0
          size: 2583MHz
          width: 64 bits
          clock: 83MHz
          capabilities: lm fpu fpu_exception wp vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp x86-64 constant_tsc arch_perfmon pebs bts rep_good nopl xtopology tsc_reliable nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 movbe popcnt tsc_deadline_timer rdrand lahf_lm 3dnowprefetch epb pti tpr_shadow vnmi flexpriority ept vpid tsc_adjust smep erms dtherm ida arat cpufreq
          configuration: cores=2 enabledcores=2 threads=2
     *-pci
          description: Host bridge
          product: Atom Processor Z36xxx/Z37xxx Series SoC Transaction Register
          vendor: Intel Corporation
          physical id: 100
          bus info: pci@0000:00:00.0
          version: 0e
          width: 32 bits
          clock: 33MHz
          configuration: driver=iosf_mbi_pci
          resources: irq:0
        *-display
             description: VGA compatible controller
             product: Atom Processor Z36xxx/Z37xxx Series Graphics & Display
             vendor: Intel Corporation
             physical id: 2
             bus info: pci@0000:00:02.0
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pm msi vga_controller bus_master cap_list rom
             configuration: driver=i915 latency=0
             resources: irq:91 memory:d0000000-d03fffff memory:c0000000-cfffffff ioport:f080(size=8) memory:c0000-dffff
        *-sata
             description: SATA controller
             product: Atom Processor E3800 Series SATA AHCI Controller
             vendor: Intel Corporation
             physical id: 13
             bus info: pci@0000:00:13.0
             logical name: scsi0
             logical name: scsi1
             version: 0e
             width: 32 bits
             clock: 66MHz
             capabilities: sata msi pm ahci_1.0 bus_master cap_list emulated
             configuration: driver=ahci latency=0
             resources: irq:90 ioport:f070(size=8) ioport:f060(size=4) ioport:f050(size=8) ioport:f040(size=4) ioport:f020(size=32) memory:d0816000-d08167ff
           *-disk
                description: ATA Disk
                product: HGST HTS545050A7
                physical id: 0
                bus info: scsi@0:0.0.0
                logical name: /dev/sda
                version: AH20
                serial: 141120TM8513TD1SRNSM
                size: 465GiB (500GB)
                capabilities: partitioned partitioned:dos
                configuration: ansiversion=5 logicalsectorsize=512 sectorsize=4096 signature=731c80f0
              *-volume:0
                   description: EXT4 volume
                   vendor: Linux
                   physical id: 1
                   bus info: scsi@0:0.0.0,1
                   logical name: /dev/sda1
                   logical name: /
                   version: 1.0
                   serial: c3a16f36-3544-4e30-8f3f-f47836ba25d4
                   size: 30GiB
                   capacity: 30GiB
                   capabilities: primary bootable journaled extended_attributes large_files huge_files dir_nlink 64bit extents ext4 ext2 initialized
                   configuration: created=2022-10-07 09:53:28 filesystem=ext4 label=Devuan lastmountpoint=/ modified=2023-05-23 13:54:09 mount.fstype=ext4 mount.options=rw,relatime,errors=remount-ro mounted=2023-05-23 11:43:58 state=mounted
              *-volume:1
                   description: Extended partition
                   physical id: 2
                   bus info: scsi@0:0.0.0,2
                   logical name: /dev/sda2
                   size: 435GiB
                   capacity: 435GiB
                   capabilities: primary extended partitioned partitioned:extended
                 *-logicalvolume:0
                      description: EXT4 volume
                      vendor: Linux
                      physical id: 5
                      logical name: /dev/sda5
                      logical name: /media/mac/Files
                      version: 1.0
                      serial: 711911f1-7502-4b4d-b9f9-2b5eb29d5081
                      size: 390GiB
                      capacity: 390GiB
                      capabilities: journaled extended_attributes large_files huge_files dir_nlink recover extents ext4 ext2 initialized
                      configuration: created=2022-09-11 21:00:32 filesystem=ext4 label=Files lastmountpoint=/media/mac/Files modified=2023-05-23 13:54:22 mount.fstype=ext4 mount.options=rw,relatime mounted=2023-05-23 13:54:22 state=mounted
                 *-logicalvolume:1
                      description: EXT4 volume
                      vendor: Linux
                      physical id: 6
                      logical name: /dev/sda6
                      logical name: /media/root/Devuan Devel
                      version: 1.0
                      serial: 7aba8942-b5cc-4d60-acc0-7e97a34a5f57
                      size: 20GiB
                      capacity: 20GiB
                      capabilities: journaled extended_attributes large_files huge_files dir_nlink recover 64bit extents ext4 ext2 initialized
                      configuration: created=2022-09-16 12:58:11 filesystem=ext4 label=Devuan Devel lastmountpoint=/media/root/Devuan Devel modified=2023-05-23 14:28:07 mount.fstype=ext4 mount.options=rw,nosuid,nodev,noexec,noatime mounted=2023-05-23 14:28:07 state=mounted
                 *-logicalvolume:2
                      description: EXT4 volume
                      vendor: Linux
                      physical id: 7
                      logical name: /dev/sda7
                      version: 1.0
                      serial: b2feaaf3-a841-41d6-9eb1-50571946d3ad
                      size: 14GiB
                      capacity: 14GiB
                      capabilities: journaled extended_attributes large_files huge_files dir_nlink recover 64bit extents ext4 ext2 initialized
                      configuration: created=2023-05-16 15:18:02 filesystem=ext4 label=Fedora lastmountpoint=/media/root/Fedora modified=2023-05-23 11:44:38 mounted=2023-05-23 11:44:38 state=clean
                 *-logicalvolume:3
                      description: EXT4 volume
                      vendor: Linux
                      physical id: 8
                      logical name: /dev/sda8
                      version: 1.0
                      serial: e2d6bbf2-9633-47ac-aeae-28e418395bf8
                      size: 9997MiB
                      capacity: 9997MiB
                      capabilities: journaled extended_attributes large_files huge_files dir_nlink 64bit extents ext4 ext2 initialized
                      configuration: created=2023-05-13 13:25:59 filesystem=ext4 label=Debian lastmountpoint=/media/root/Debian modified=2023-05-23 11:30:45 mounted=2023-05-23 11:00:52 state=clean
           *-cdrom
                description: DVD-RAM writer
                product: CDDVDW SU-208FB
                vendor: TSSTcorp
                physical id: 1
                bus info: scsi@1:0.0.0
                logical name: /dev/cdrom
                logical name: /dev/cdrw
                logical name: /dev/dvd
                logical name: /dev/dvdrw
                logical name: /dev/sr0
                version: TF01
                capabilities: removable audio cd-r cd-rw dvd dvd-r dvd-ram
                configuration: ansiversion=5 status=nodisc
        *-usb
             description: USB controller
             product: Atom Processor Z36xxx/Z37xxx, Celeron N2000 Series USB xHCI
             vendor: Intel Corporation
             physical id: 14
             bus info: pci@0000:00:14.0
             version: 0e
             width: 64 bits
             clock: 33MHz
             capabilities: pm msi xhci bus_master cap_list
             configuration: driver=xhci_hcd latency=0
             resources: irq:93 memory:d0800000-d080ffff
        *-generic
             description: Encryption controller
             product: Atom Processor Z36xxx/Z37xxx Series Trusted Execution Engine
             vendor: Intel Corporation
             physical id: 1a
             bus info: pci@0000:00:1a.0
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pm msi bus_master cap_list
             configuration: driver=mei_txe latency=0
             resources: irq:92 memory:d0500000-d05fffff memory:d0400000-d04fffff
        *-multimedia
             description: Audio device
             product: Atom Processor Z36xxx/Z37xxx Series High Definition Audio Controller
             vendor: Intel Corporation
             physical id: 1b
             bus info: pci@0000:00:1b.0
             version: 0e
             width: 64 bits
             clock: 33MHz
             capabilities: pm msi bus_master cap_list
             configuration: driver=snd_hda_intel latency=0
             resources: irq:95 memory:d0810000-d0813fff
        *-pci:0
             description: PCI bridge
             product: Atom Processor E3800 Series PCI Express Root Port 1
             vendor: Intel Corporation
             physical id: 1c
             bus info: pci@0000:00:1c.0
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
             configuration: driver=pcieport
             resources: irq:87 ioport:1000(size=4096)
        *-pci:1
             description: PCI bridge
             product: Atom Processor E3800 Series PCI Express Root Port 2
             vendor: Intel Corporation
             physical id: 1c.1
             bus info: pci@0000:00:1c.1
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
             configuration: driver=pcieport
             resources: irq:88 ioport:2000(size=4096) memory:d0700000-d07fffff
           *-network
                description: Wireless interface
                product: AR9485 Wireless Network Adapter
                vendor: Qualcomm Atheros
                physical id: 0
                bus info: pci@0000:02:00.0
                logical name: wlan0
                version: 01
                serial: ac:b5:7d:90:83:9f
                width: 64 bits
                clock: 33MHz
                capabilities: pm msi pciexpress bus_master cap_list rom ethernet physical wireless
                configuration: broadcast=yes driver=ath9k driverversion=5.10.0-23-amd64 firmware=N/A ip=192.168.1.69 latency=0 link=yes multicast=yes wireless=IEEE 802.11
                resources: irq:17 memory:d0700000-d077ffff memory:d0780000-d078ffff
        *-pci:2
             description: PCI bridge
             product: Atom Processor E3800 Series PCI Express Root Port 3
             vendor: Intel Corporation
             physical id: 1c.2
             bus info: pci@0000:00:1c.2
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pci pciexpress msi pm normal_decode bus_master cap_list
             configuration: driver=pcieport
             resources: irq:89 ioport:3000(size=4096) memory:d0600000-d06fffff
           *-generic
                description: Unassigned class
                product: RTS5229 PCI Express Card Reader
                vendor: Realtek Semiconductor Co., Ltd.
                physical id: 0
                bus info: pci@0000:03:00.0
                version: 01
                width: 32 bits
                clock: 33MHz
                capabilities: pm msi pciexpress bus_master cap_list
                configuration: driver=rtsx_pci latency=0
                resources: irq:94 memory:d0600000-d0600fff
        *-isa
             description: ISA bridge
             product: Atom Processor Z36xxx/Z37xxx Series Power Control Unit
             vendor: Intel Corporation
             physical id: 1f
             bus info: pci@0000:00:1f.0
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: isa bus_master cap_list
             configuration: driver=lpc_ich latency=0
             resources: irq:0
        *-serial
             description: SMBus
             product: Atom Processor E3800 Series SMBus Controller
             vendor: Intel Corporation
             physical id: 1f.3
             bus info: pci@0000:00:1f.3
             version: 0e
             width: 32 bits
             clock: 33MHz
             capabilities: pm cap_list
             configuration: driver=i801_smbus latency=0
             resources: irq:18 memory:d0814000-d081401f ioport:f000(size=32)
     *-pnp00:00
          product: PnP device PNP0b00
          physical id: 1
          capabilities: pnp
          configuration: driver=rtc_cmos
     *-pnp00:01
          product: PnP device PNP0c02
          physical id: 2
          capabilities: pnp
          configuration: driver=system
     *-pnp00:02
          product: PnP device TOS0330
          physical id: 3
          capabilities: pnp
          configuration: driver=i8042 aux
     *-pnp00:03
          product: PnP device TOS1106
          physical id: 4
          capabilities: pnp
          configuration: driver=i8042 kbd
     *-pnp00:04
          product: PnP device PNP0c02
          physical id: 5
          capabilities: pnp
          configuration: driver=system

As you can see, this computer is not precisely high-end, so here's my question:

I'm considering creating a small music-dedicated live iso to run on ram (based on slax, since av linux is quite heavy on resources).
Before compiling a low-latency kernel to go with it, I'd like to know if such kernel would be worth the trouble running on my hardware.

Thanks for your feedback.

[Musicteacher]

Probably noone will be able to tell in advance if it will make a difference for you.

Also, you won't notice a difference when using a realtime kernel without making further adjustments.

Most people here use Jack, and try out different buffer sizes and then use the lowest buffer size which doesn't give xruns (dropouts).

So it might be that with a vanilla kernel you can have 256 pages buffer size, no dropouts, and with a rt-kernel , 128 pages buffer size. But if you leave your other settings as they are, you wil have exactly the same latency with a rt-kernel as with a vanilla kernel.

Are you using jack?

[Impostor]

Before compiling a low-latency kernel to go with it, I'd like to know if such kernel would be worth the trouble running on my hardware.

Thanks for your feedback.

Have you optimized your system for audio? If you do that there's probably no need for a low latency, let alone a real time, kernel. The following steps are working on my system (mint, so probably also for ubuntu and devian):

1. Add yourself to the audio group:

   Code: Select all

   sudo usermod -a -G audio username

2. To /etc/sysctl.conf, add:

   Code: Select all

    fs.inotify.max_user_watches = 524288
    vm.swappiness=10 

3. /etc/security/limits.conf or /etc/security/limits.d/audio.conf should contain something like:

   Code: Select all

    @audio - rtprio 90       # maximum realtime priority
    @audio - memlock unlimited  # maximum locked-in-memory address space (KB)
   

4. Open /etc/default/grub. Look for GRUB_CMDLINE_LINUX_DEFAULT and add threadirqs to the list of options:

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   GRUB_CMDLINE_LINUX_DEFAULT="quiet splash threadirqs"
   

   Save the file and update the grub configuration:

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   sudo update-grub
   

   Reboot.

5. Optionally (to prevent x-runs if they bother you) you could set your CPUs to performance. But that may not even be needed with new CPUs. (since I upgraded to AMD 5600X I almost never need to do this anymore)

6. Use qjackctl to optimize jack settings for latency: set your buffer (too small will give distorted audio. too large gives too much latency) Do not set it smaller than you need though since this will tax your CPU unnecessarily. Set it to run realtime.

[amc252]

Are you using jack?

Thanks for the suggestions. I'm trying different setups, with and without jack.
That's why I installed a fresh Devuan system in a separated partition, so I can tinker and experiment with it without screwing up my working distro.

Have you optimized your system for audio?

Not yet, but that's the idea.
I'm very new to linux audio, still at the beginning of my journey and all of your suggestions are precious.
So far, after learning how to connect everything (mainly fluidsynth and linuxsamper) all I did was trying out different soundfonts and SFZ piano samples, some lighter than others.

[onefang]

Hello everybody,

I have set up a minimal devuan system on a spare partition to play around with music.
If I play my midi keyboard with fluidsynth there is no noticeable latency, but if I play it with linuxsampler I can see a slight delay.
So, I have installed a second kernel, low-latency liquorix-6.0.0-10.1-amd64 to see if it would improve performance.

Devuan has a RT kernel. It's what I use.

[amc252]

Thanks again for the suggestions.

Devuan has a RT kernel. It's what I use.

Yes, I installed that too but haven't tried it yet.

To /etc/sysctl.conf, add:

Code: Select all

fs.inotify.max_user_watches = 524288
 vm.swappiness=10

I added the first line. Not having swap I assume the second is unnecessary.

/etc/security/limits.conf or /etc/security/limits.d/audio.conf should contain something like:

Code: Select all

@audio - rtprio 90       # maximum realtime priority
 @audio - memlock unlimited  # maximum locked-in-memory address space (KB)

my /etc/security/limits.conf has:

Code: Select all

@audio - rtprio 90
@audio - nice -10
@audio - memlock 500000

and /etc/security/limits.d/audio.conf has:

Code: Select all

@audio   -  rtprio     95
@audio   -  memlock    unlimited

Should I use only one setting?

[Impostor]

my /etc/security/limits.conf has:

Code: Select all

@audio - rtprio 90
@audio - nice -10
@audio - memlock 500000

and /etc/security/limits.d/audio.conf has:

Code: Select all

@audio   -  rtprio     95
@audio   -  memlock    unlimited

Should I use only one setting?

The settings in the limits.d/audio.conf file seemingly have precedence over those in the other file. So it's ok like that. And the niceness setting is irrelevant for realtime processes, if I remember correctly.

And it's not clear to me if setting swappiness has any effect at all, even if you do have a swap partition. I just copied those instructions from somewhere a couple of years ago. Some may have become obsolete.

[amc252]

Well, I tried Impostor's setting and the Devuan RT kernel, and YES, there's a great difference.

I recorded video and audio in OBS Studio, trying both Linuxsampler + Amethyst Imperial Grand - Imperial Hall.sfz soundfonts, and also Pianoteq Grand Piano.
The latency that was very annoying in my previous recording is now down to negligible.
Also the cracking noises are completely gone, and the sound quality is rather good.

[amc252]

So it might be that with a vanilla kernel you can have 256 pages buffer size, no dropouts, and with a rt-kernel , 128 pages buffer size. But if you leave your other settings as they are, you wil have exactly the same latency with a rt-kernel as with a vanilla kernel.

You might be underestimating my ignorance.
When you say 'page buffer size' are you referring to the Frames/period setting in qjackctl parameters?

[Musicteacher]

So it might be that with a vanilla kernel you can have 256 pages buffer size, no dropouts, and with a rt-kernel , 128 pages buffer size. But if you leave your other settings as they are, you wil have exactly the same latency with a rt-kernel as with a vanilla kernel.

You might be underestimating my ignorance.
When you say 'page buffer size' are you referring to the Frames/period setting in qjackctl parameters?

Yes, but I got that wrong myself, it's "frames", not pages.

[amc252]

Thanks!
Little by little I'm getting there.
This forum is wonderful.