Re: [PATCH 1/1] bcache: allow user to set QUEUE_FLAG_NOWAIT

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On 5/13/23 14:30, Eric Wheeler wrote:
> On Fri, 12 May 2023, Chaitanya Kulkarni wrote:
>> Allow user to set the QUEUE_FLAG_NOWAIT optionally using module
>> parameter to retain the default behaviour. Also, update respective
>> allocation flags in the write path. Following are the performance
>> numbers with io_uring fio engine for random read, note that device has
>> been populated fully with randwrite workload before taking these
>> numbers :-
>> * linux-block (for-next) # grep IOPS  bc-*fio | column -t
>> nowait-off-1.fio:  read:  IOPS=482k,  BW=1885MiB/s
>> nowait-off-2.fio:  read:  IOPS=484k,  BW=1889MiB/s
>> nowait-off-3.fio:  read:  IOPS=483k,  BW=1886MiB/s
>> nowait-on-1.fio:   read:  IOPS=544k,  BW=2125MiB/s
>> nowait-on-2.fio:   read:  IOPS=547k,  BW=2137MiB/s
>> nowait-on-3.fio:   read:  IOPS=546k,  BW=2132MiB/s
>> * linux-block (for-next) # grep slat  bc-*fio | column -t
>> nowait-off-1.fio: slat (nsec):  min=430, max=5488.5k, avg=2797.52
>> nowait-off-2.fio: slat (nsec):  min=431, max=8252.4k, avg=2805.33
>> nowait-off-3.fio: slat (nsec):  min=431, max=6846.6k, avg=2814.57
>> nowait-on-1.fio:  slat (usec):  min=2,   max=39086,   avg=87.48
>> nowait-on-2.fio:  slat (usec):  min=3,   max=39519,   avg=86.98
>> nowait-on-3.fio:  slat (usec):  min=3,   max=38880,   avg=87.17
>> * linux-block (for-next) # grep cpu  bc-*fio | column -t
>> nowait-off-1.fio:  cpu  :  usr=2.77%,  sys=6.57%,   ctx=22015526
>> nowait-off-2.fio:  cpu  :  usr=2.75%,  sys=6.59%,   ctx=22003700
>> nowait-off-3.fio:  cpu  :  usr=2.81%,  sys=6.57%,   ctx=21938309
>> nowait-on-1.fio:   cpu  :  usr=1.08%,  sys=78.39%,  ctx=2744092
>> nowait-on-2.fio:   cpu  :  usr=1.10%,  sys=79.76%,  ctx=2537466
>> nowait-on-3.fio:   cpu  :  usr=1.10%,  sys=79.88%,  ctx=2528092
> Wow, amazing for such a tiny patch.  Especially the latency numbers! Given
> this, maybe NOWAIT should be enabled by default.

yes, sending out V2 without the module parameter as my other patches
has similar comment to enable nowait by default.

> Why would anyone want to use the old NOWAIT=off variant?

for some reason I wanted to make it backward compatible just in case
this change creates regression on the setup that I don't have access to ..

> Are there benefits to going without NOWAIT that go unnoticed when testing
> against a ramdisk?

no not at all from what I can see ramdisk enables it by default ..

> For example, (and this seems unlikely) can NOWAIT affect the IO scheduler
> in a way that would prevent sorted IOs headed toward a rotational disk?

unfortunately I don't have a setup to run those tests :(.

> It would be interesting to see two more test classes:
> 1. Ram disk cache with NVMe backing device.
> 2. NVMe cache with rotational HDD backing device.
> -Eric

once I get a setup I'll be happy to run those numbers ..


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Index of Archives]     [Linux ARM Kernel]     [Linux Filesystem Development]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Security]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [ECOS]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux