From: Jens Axboe <axboe@kernel.dk>
To: "Srivatsa S. Bhat" <srivatsa@csail.mit.edu>, Jan Kara <jack@suse.cz>
Cc: Paolo Valente <paolo.valente@linaro.org>,
linux-fsdevel@vger.kernel.org,
linux-block <linux-block@vger.kernel.org>,
linux-ext4@vger.kernel.org, cgroups@vger.kernel.org,
kernel list <linux-kernel@vger.kernel.org>,
Jeff Moyer <jmoyer@redhat.com>, Theodore Ts'o <tytso@mit.edu>,
amakhalov@vmware.com, anishs@vmware.com, srivatsab@vmware.com,
Ulf Hansson <ulf.hansson@linaro.org>,
Linus Walleij <linus.walleij@linaro.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Stable <stable@vger.kernel.org>
Subject: Re: CFQ idling kills I/O performance on ext4 with blkio cgroup controller
Date: Thu, 13 Jun 2019 02:37:29 -0600 [thread overview]
Message-ID: <aca00f05-4d71-7db0-52d6-7aa0932cc5c0@kernel.dk> (raw)
In-Reply-To: <dd32ed59-a543-fc76-9a9a-2462f0119270@csail.mit.edu>
On 6/12/19 1:36 PM, Srivatsa S. Bhat wrote:
>
> [ Adding Greg to CC ]
>
> On 6/12/19 6:04 AM, Jan Kara wrote:
>> On Tue 11-06-19 15:34:48, Srivatsa S. Bhat wrote:
>>> On 6/2/19 12:04 AM, Srivatsa S. Bhat wrote:
>>>> On 5/30/19 3:45 AM, Paolo Valente wrote:
>>>>>
>>> [...]
>>>>> At any rate, since you pointed out that you are interested in
>>>>> out-of-the-box performance, let me complete the context: in case
>>>>> low_latency is left set, one gets, in return for this 12% loss,
>>>>> a) at least 1000% higher responsiveness, e.g., 1000% lower start-up
>>>>> times of applications under load [1];
>>>>> b) 500-1000% higher throughput in multi-client server workloads, as I
>>>>> already pointed out [2].
>>>>>
>>>>
>>>> I'm very happy that you could solve the problem without having to
>>>> compromise on any of the performance characteristics/features of BFQ!
>>>>
>>>>
>>>>> I'm going to prepare complete patches. In addition, if ok for you,
>>>>> I'll report these results on the bug you created. Then I guess we can
>>>>> close it.
>>>>>
>>>>
>>>> Sounds great!
>>>>
>>>
>>> Hi Paolo,
>>>
>>> Hope you are doing great!
>>>
>>> I was wondering if you got a chance to post these patches to LKML for
>>> review and inclusion... (No hurry, of course!)
>>>
>>> Also, since your fixes address the performance issues in BFQ, do you
>>> have any thoughts on whether they can be adapted to CFQ as well, to
>>> benefit the older stable kernels that still support CFQ?
>>
>> Since CFQ doesn't exist in current upstream kernel anymore, I seriously
>> doubt you'll be able to get any performance improvements for it in the
>> stable kernels...
>>
>
> I suspected as much, but that seems unfortunate though. The latest LTS
> kernel is based on 4.19, which still supports CFQ. It would have been
> great to have a process to address significant issues on older
> kernels too.
>
> Greg, do you have any thoughts on this? The context is that both CFQ
> and BFQ I/O schedulers have issues that cause I/O throughput to suffer
> upto 10x - 30x on certain workloads and system configurations, as
> reported in [1].
>
> In this thread, Paolo posted patches to fix BFQ performance on
> mainline. However CFQ suffers from the same performance collapse, but
> CFQ was removed from the kernel in v5.0. So obviously the usual stable
> backporting path won't work here for several reasons:
>
> 1. There won't be a mainline commit to backport from, as CFQ no
> longer exists in mainline.
>
> 2. This is not a security/stability fix, and is likely to involve
> invasive changes.
>
> I was wondering if there was a way to address the performance issues
> in CFQ in the older stable kernels (including the latest LTS 4.19),
> despite the above constraints, since the performance drop is much too
> significant. I guess not, but thought I'd ask :-)
>
> [1]. https://lore.kernel.org/lkml/8d72fcf7-bbb4-2965-1a06-e9fc177a8938@csail.mit.edu/
This issue has always been there. There will be no specific patches made
for stable for something that doesn't even exist in the newer kernels.
--
Jens Axboe
next prev parent reply other threads:[~2019-06-13 16:23 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-17 22:16 CFQ idling kills I/O performance on ext4 with blkio cgroup controller Srivatsa S. Bhat
2019-05-18 18:39 ` Paolo Valente
2019-05-18 19:28 ` Theodore Ts'o
2019-05-20 9:15 ` Jan Kara
2019-05-20 10:45 ` Paolo Valente
2019-05-21 16:48 ` Theodore Ts'o
2019-05-21 18:19 ` Josef Bacik
2019-05-21 19:10 ` Theodore Ts'o
2019-05-20 10:38 ` Paolo Valente
2019-05-21 7:38 ` Andrea Righi
2019-05-18 20:50 ` Srivatsa S. Bhat
2019-05-20 10:19 ` Paolo Valente
2019-05-20 22:45 ` Srivatsa S. Bhat
2019-05-21 6:23 ` Paolo Valente
2019-05-21 7:19 ` Srivatsa S. Bhat
2019-05-21 9:10 ` Jan Kara
2019-05-21 16:31 ` Theodore Ts'o
2019-05-21 11:25 ` Paolo Valente
2019-05-21 13:20 ` Paolo Valente
2019-05-21 16:21 ` Paolo Valente
2019-05-21 17:38 ` Paolo Valente
2019-05-21 22:51 ` Srivatsa S. Bhat
2019-05-22 8:05 ` Paolo Valente
2019-05-22 9:02 ` Srivatsa S. Bhat
2019-05-22 9:12 ` Paolo Valente
2019-05-22 10:02 ` Srivatsa S. Bhat
2019-05-22 9:09 ` Paolo Valente
2019-05-22 10:01 ` Srivatsa S. Bhat
2019-05-22 10:54 ` Paolo Valente
2019-05-23 2:30 ` Srivatsa S. Bhat
2019-05-23 9:19 ` Paolo Valente
2019-05-23 17:22 ` Paolo Valente
2019-05-23 23:43 ` Srivatsa S. Bhat
2019-05-24 6:51 ` Paolo Valente
2019-05-24 7:56 ` Paolo Valente
2019-05-29 1:09 ` Srivatsa S. Bhat
2019-05-29 7:41 ` Paolo Valente
2019-05-30 8:29 ` Srivatsa S. Bhat
2019-05-30 10:45 ` Paolo Valente
2019-06-02 7:04 ` Srivatsa S. Bhat
2019-06-11 22:34 ` Srivatsa S. Bhat
2019-06-12 13:04 ` Jan Kara
2019-06-12 19:36 ` Srivatsa S. Bhat
2019-06-13 6:02 ` Greg Kroah-Hartman
2019-06-13 19:03 ` Srivatsa S. Bhat
2019-06-13 8:20 ` Jan Kara
2019-06-13 19:05 ` Srivatsa S. Bhat
2019-06-13 8:37 ` Jens Axboe [this message]
2019-06-13 5:46 ` Paolo Valente
2019-06-13 19:13 ` Srivatsa S. Bhat
2019-05-23 23:32 ` Srivatsa S. Bhat
2019-05-30 8:38 ` Srivatsa S. Bhat
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