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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


  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 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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