linux-kernel - Re: This is the fourth time I’ve tried to find what led to the regression of outgoing network speed and each time I find the merge commit 8c94ccc7cd691472461448f98e2372c75849406c

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Message-ID: <43a769dd-aa09-4da3-a226-ecef98f32e0f@infradead.org>
Date: Fri, 2 Feb 2024 17:15:30 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>,
 Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
 linux-netdev@...r.kernel.org, Greg KH <gregkh@...uxfoundation.org>
Subject: Re: This is the fourth time I’ve tried to find what led to the regression of outgoing network speed and each time I find the merge commit 8c94ccc7cd691472461448f98e2372c75849406c

Hi,

On 2/2/24 17:02, Mikhail Gavrilov wrote:
> Hi,
> I'm trying to find the first bad commit that led to a decreased
> network outgoing speed.
> And every time I come to a huge merge [Merge tag 'usb-6.8-rc1' of
> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb]
> I have already triple-checked all my answers and speed measurements.
> I don't understand where I'm making a mistake.
> 
> Let's try to figure it out together.
> 
> Input data:
> Two computers connected 1Gbps link.
> Both have the same hardware.
> Network: RTL8125 2.5GbE Controller (rev 05)
> 
> When I copy files from one computer to another and kernel snapshot
> builded from commit 296455ade1fd I have 97-110MB/sec which is almost
> max speed of 1Gbps link.
> When I move to commit 9d1694dc91ce I have only 66-70MB/sec which is
> significantly slower.
> 
> I bisected the issue by measuring network speed on each step.
> I save all results to file [1]
> 
> [1] file is attached as a zip archive.
> 
> # first bad commit: [8c94ccc7cd691472461448f98e2372c75849406c] Merge
> tag 'usb-6.8-rc1' of
> git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb

a. Do you clean the object files between each test run?
or at least clean net/* and drivers/net/ethernet/* ?

b. I am far from a git expert, but in the bisects that I have
done, after each test run, I just say
$ git bisect good
or
$ git bisect bad

It looks like you are typing
$ git bisect [good | bad] hashID

Is that correct?

Anyway, I am interested in your outcome just to learn
how to handle this problem.

Good luck.

-- 
#Randy