linux-kernel - Re: [REGRESSION]: mmap performance regression starting with k-6.1

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Date:   Thu, 23 Nov 2023 03:06:42 +0000
From:   Chun Ng <chunn@...dia.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:     Linux Regressions <regressions@...ts.linux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Ankita Garg <ankitag@...dia.com>
Subject: Re: [REGRESSION]: mmap performance regression starting with k-6.1

>> Did you mean that v6.0 doesn't have this regression?

No, k-6.0 does NOT have this regression. The regression starts from k-6.1.

Best,
Chun

From: Bagas Sanjaya
Sent: Wednesday, November 22, 2023 5:18 PM
To: Chun Ng; Linux Kernel Mailing List
Cc: Linux Regressions; Andrew Morton; Linux Memory Management List; Liam R. Howlett; Ankita Garg
Subject: Re: [REGRESSION]: mmap performance regression starting with k-6.1


On Wed, Nov 22, 2023 at 08:03:19PM +0000, Chun Ng wrote:

> Hi,

>

> Recently I observed there is performance regression on system call mmap(..). I tried both vanilla kernels and Raspberry Pi kernels on a Raspberry Pi 4 box and the results are pretty consistent among them.

>

> Bisection showed that the regression starts from k-6.1, and the latest vanilla k-6.7 is still showing the same regression.

>

> The test program calls mmap/munmap for a 4K page with MAP_ANON and MAP_PRIVATE flags, and ftrace is used to measure the time spent on the do_mmap(..) call.  Measured time of a sample run with different vanilla kernel versions are:

> k-5.10 and k-6.0: ~157us

> k-6.1: ~194us

> k-6.7: ~214us

> Results are pretty consistent across multiple runs with a small percentage variance.  Ftrace shows that latency of mmap_region(...) has increased since k-6.1.  An application that makes frequent mmap(..) calls the accumulated extra latency is very noticeable.



Did you mean that v6.0 doesn't have this regression?



Confused...



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