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

From: mikhail.v.gavrilov@gmail.com
To: Thomas Gleixner <tglx@linutronix.de>,
	Mathias Nyman <mathias.nyman@linux.intel.com>,
	Linux regressions mailing list <regressions@lists.linux.dev>
Cc: "Christian A. Ehrhardt" <lk@c--e.de>,
	niklas.neronin@linux.intel.com,
	 Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,  x86@kernel.org,
	netdev@vger.kernel.org, Randy Dunlap <rdunlap@infradead.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
Date: Tue, 27 Feb 2024 22:08:20 +0500	[thread overview]
Message-ID: <098670097a6fd59f3e254c5294882f3fa12e3c65.camel@gmail.com> (raw)
In-Reply-To: <87r0gz9jxp.ffs@tglx>

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On Mon, 2024-02-26 at 19:09 +0100, Thomas Gleixner wrote:
> we don't have any information about the overall workload,

During measurements nothing was running except iperf3

> other interrupt sources on CPU0 and their frequency. That'd need to
> be investigated with instrumentation and might unearth some
> completely different underlying reason causing this behavior.

I made simple bash script for benchmark enp14s0 on each of CPU core.

#!/usr/bin/env bash
for i in {0..31}
do
	smp_affinity=$(echo 'obase=16; '$((2 ** i)) | bc)
	echo "echo $smp_affinity > /proc/irq/84/smp_affinity"
	echo $smp_affinity > /proc/irq/84/smp_affinity
	echo 'iperf3 -c primary-ws.local -t 5 -p 5000 -P 1'
	iperf3 -c primary-ws.local -t 5 -p 5000 -P 1
done

And attach here results of iperf3 for kernels 6.7.0 and 6.8.0-rc6.
Which once again makes sure that CPU0 is a bad option in both cases.
And any other CPU does not necessarily 23 allow the network interface
to operate at the limit of the capabilities of the network cable.

I also attach /proc/interrupts I hope this helps clear things up.

I don't know how else to help you. What information to provide.

About repeatability my "unlucky" scenario.
I have two MSI MPG B650I EDGE WIFI motherboards and this problem
happened both at the same time.

It seems the problem has always been there, we just never noticed it.

-- 
Best Regards,
Mike Gavrilov.

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