From: Chaitanya Kulkarni <chaitanyak@nvidia.com>
To: Eric Wheeler <bcache@lists.ewheeler.net>,
Chaitanya Kulkarni <chaitanyak@nvidia.com>
Cc: "colyli@suse.de" <colyli@suse.de>,
"kent.overstreet@gmail.com" <kent.overstreet@gmail.com>,
"linux-bcache@vger.kernel.org" <linux-bcache@vger.kernel.org>
Subject: Re: [PATCH 1/1] bcache: allow user to set QUEUE_FLAG_NOWAIT
Date: Sat, 13 May 2023 22:51:21 +0000 [thread overview]
Message-ID: <abd5b7bc-2b39-af7c-9593-dcb1a7af879a@nvidia.com> (raw)
In-Reply-To: <31bfee17-47f0-b1ca-eb0-baf0762b41e8@ewheeler.net>
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 ..
-ck
prev parent reply other threads:[~2023-05-13 22:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-12 9:54 [PATCH 0/1] bcache: allow user to set QUEUE_FLAG_NOWAIT Chaitanya Kulkarni
2023-05-12 9:54 ` [PATCH 1/1] " Chaitanya Kulkarni
2023-05-13 21:30 ` Eric Wheeler
2023-05-13 22:51 ` Chaitanya Kulkarni [this message]
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