Re: [External] : Re: [bug-report] 5-9% FIO randomwrite ext4 perf regression on 6.12.y kernel

[Phil Auld <pauld@redhat.com>]

On Thu, Nov 21, 2024 at 09:07:32PM +0000 Paul Webb wrote:
> Hi,
> 
> To answer the various questions/suggestions, I'll just group them here:
> 
> Phil:
> can you try your randwrite test after
> "echo NO_DELAY_DEQUEUE > /sys/kernel/debug/sched/features"
> 
> Performance regression still persists with this setting being used.
>

Okay, thanks. Different FIO randwrite issue I guess.  Nevermind, I'll
go back over to scheduler land...



Cheers,
Phil

> 
> Christoph:
> To check for weird lazy init code using write zeroes
> 
> Values in the 5.15 kernel baseline prior to the commit:
> $ cat /sys/block/nvme*n1/queue/write_zeroes_max_bytes
> 0
> 0
> 0
> 0
> 
> Values in the 6.11 kernel that contains the commit:
> $ cat /sys/block/nvme*n1/queue/write_zeroes_max_bytes
> 2199023255040
> 2199023255040
> 2199023255040
> 2199023255040
> 
> 
> 
> Chaitanya:
> 
> Run the same test on the  XFS formatted nvme device instead of ext4 ?
> - XFS runs did not show the performance regression.
> 
> Run the same test on the raw nvme device /dev/nvme0n1 that you    have used for
> this benchmark
> - Will have to check if this was done, and if not, get that test run
> 
> repeat these numbers for io_uring fio io_engine
> - Will look into getting those too
> 
> 
> Another interesting datapoint is that while performing some runs I am seeing
> the following output on the console in the 6.11/6.12 kernels that contain the
> commit:
> 
> [  473.398188] operation not supported error, dev nvme2n1, sector 13952 op 0x9:(WRITE_ZEROES) flags 0x800 phys_seg 0 prio class 0
> [  473.534550] nvme0n1: Dataset Management(0x9) @ LBA 14000, 256 blocks, Invalid Command Opcode (sct 0x0 / sc 0x1) DNR
> [  473.660502] operation not supported error, dev nvme0n1, sector 14000 op 0x9:(WRITE_ZEROES) flags 0x800 phys_seg 0 prio class 0
> [  473.796859] nvme3n1: Dataset Management(0x9) @ LBA 13952, 256 blocks, Invalid Command Opcode (sct 0x0 / sc 0x1) DNR
> [  473.922810] operation not supported error, dev nvme3n1, sector 13952 op 0x9:(WRITE_ZEROES) flags 0x800 phys_seg 0 prio class 0
> [  474.059169] nvme1n1: Dataset Management(0x9) @ LBA 13952, 256 blocks, Invalid Command Opcode (sct 0x0 / sc 0x1) DNR
> 
> 
> Regards,
> Paul.
> 
> 
> 
> On 21/11/2024 14:49, Jens Axboe wrote:
> 
>     On 11/21/24 4:30 AM, Phil Auld wrote:
> 
>         Hi,
> 
>         On Wed, Nov 20, 2024 at 06:20:12PM -0700 Jens Axboe wrote:
> 
>             On 11/20/24 5:00 PM, Chaitanya Kulkarni wrote:
> 
>                 On 11/20/24 13:35, Saeed Mirzamohammadi wrote:
> 
>                     Hi,
> 
>                     I?m reporting a performance regression of up to 9-10% with FIO randomwrite benchmark on ext4 comparing 6.12.0-rc2 kernel and v5.15.161. Also, standard deviation after this change grows up to 5-6%.
> 
>                     Bisect root cause commit
>                     ===================
>                     - commit 63dfa1004322 ("nvme: move NVME_QUIRK_DEALLOCATE_ZEROES out of nvme_config_discard?)
> 
> 
>                     Test details
>                     =========
>                     - readwrite=randwrite bs=4k size=1G ioengine=libaio iodepth=16 direct=1 time_based=1 ramp_time=180 runtime=1800 randrepeat=1 gtod_reduce=1
>                     - Test is on ext4 filesystem
>                     - System has 4 NVMe disks
> 
> 
>                 Thanks a lot for the report, to narrow down this problem can you
>                 please :-
> 
>                 1. Run the same test on the raw nvme device /dev/nvme0n1 that you
>                     have used for this benchmark ?
>                 2. Run the same test on the  XFS formatted nvme device instead of ext4 ?
> 
>                 This way we will know if there is an issue only with the ext4 or
>                 with other file systems are suffering from this problem too or
>                 it is below the file system layer such as block layer and nvme pci driver ?
> 
>                 It will also help if you can repeat these numbers for io_uring fio io_engine
>                 to narrow down this problem to know if the issue is ioengine specific.
> 
>                 Looking at the commit [1], it only sets the max value to write zeroes
>                 sectors
>                 if NVME_QUIRK_DEALLOCATE_ZEROES is set, else uses the controller max
>                 write zeroes value.
> 
>             There's no way that commit is involved, the test as quoted doesn't even
>             touch write zeroes. Hence if there really is a regression here, then
>             it's either not easily bisectable, some error was injected while
>             bisecting, or the test itself is bimodal.
> 
>         I was just going to ask how confident we are in that bisect result.
> 
>         I suspect this is the same issue I've been fighting here:
> 
>         [1]https://urldefense.com/v3/__https://lore.kernel.org/lkml/20241101124715.GA689589@pauld.westford.csb/__;!!ACWV5N9M2RV99hQ!PXJXp0zosonkV7jeW9yE0YL-uPElcYI-G-bvm69COWR1Tbl9w9puGc1tLR_ccsDoYPBb9Bs3waNVuuf9Lg$
> 
>         Saeed, can you try your randwrite test after
> 
>           "echo NO_DELAY_DEQUEUE > /sys/kernel/debug/sched/features"
> 
>         please?
> 
>         We don't as yet have a general fix for it as it seems to be a bit of
>         a trade off.
> 
>     Interesting. Might explain some regressions I've seen too related to
>     performance.
> 
> 
> 
> References:
> 
> [1] https://urldefense.com/v3/__https://lore.kernel.org/lkml/20241101124715.GA689589@pauld.westford.csb/__;!!ACWV5N9M2RV99hQ!PXJXp0zosonkV7jeW9yE0YL-uPElcYI-G-bvm69COWR1Tbl9w9puGc1tLR_ccsDoYPBb9Bs3waNVuuf9Lg$

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