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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Date: Wed, 7 Feb 2024 16:55:17 +0500
From: Mikhail Gavrilov <mikhail.v.gavrilov@...il.com>
To: Mathias Nyman <mathias.nyman@...ux.intel.com>
Cc: "Christian A. Ehrhardt" <lk@...e.de>, niklas.neronin@...ux.intel.com, 
	Linux List Kernel Mailing <linux-kernel@...r.kernel.org>, Greg KH <gregkh@...uxfoundation.org>, 
	linux-usb@...r.kernel.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

On Wed, Feb 7, 2024 at 3:39 PM Mathias Nyman
<mathias.nyman@...ux.intel.com> wrote:
>
> Thanks,
>
> Looks like your network adapter ends up interrupting CPU0 in the bad case due
> to the change in how many interrupts are requested by xhci_hcd before it.
>
> bad case:
>         CPU0    CPU1    ...     CPU31
> 87:     18213809 0      ...     0       IR-PCI-MSIX-0000:0e:00.0    0-edge      enp14s0
>
> Does manually changing it to some other CPU help? picking one that doesn't already
> handle a lot of interrupts. CPU0 could also in general be more busy, possibly spending
> more time with interrupts disabled.
>
> For example change to CPU23 in the bad case:
>
> echo 800000 > /proc/irq/87/smp_affinity
>
> Check from proc/interrupts that enp14s0 interrupts actually go to CPU23 after this.
>
> Thanks
> Mathias
>

root@...ondary-ws ~# iperf3 -c primary-ws.local -t 5 -p 5000 -P 1
Connecting to host primary-ws.local, port 5000
[  5] local 192.168.1.130 port 49152 connected to 192.168.1.96 port 5000
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  70.9 MBytes   594 Mbits/sec    0    376 KBytes
[  5]   1.00-2.00   sec  72.4 MBytes   607 Mbits/sec    0    431 KBytes
[  5]   2.00-3.00   sec  73.1 MBytes   613 Mbits/sec    0    479 KBytes
[  5]   3.00-4.00   sec  72.4 MBytes   607 Mbits/sec    0    501 KBytes
[  5]   4.00-5.00   sec  73.2 MBytes   614 Mbits/sec    0    501 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-5.00   sec   362 MBytes   607 Mbits/sec    0             sender
[  5]   0.00-5.00   sec   360 MBytes   603 Mbits/sec                  receiver

iperf Done.
root@...ondary-ws ~# echo 800000 > /proc/irq/87/smp_affinity
root@...ondary-ws ~# iperf3 -c primary-ws.local -t 5 -p 5000 -P 1
Connecting to host primary-ws.local, port 5000
[  5] local 192.168.1.130 port 37620 connected to 192.168.1.96 port 5000
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   111 MBytes   934 Mbits/sec    0    621 KBytes
[  5]   1.00-2.00   sec   109 MBytes   913 Mbits/sec    0    621 KBytes
[  5]   2.00-3.00   sec   110 MBytes   920 Mbits/sec    0    621 KBytes
[  5]   3.00-4.00   sec   110 MBytes   924 Mbits/sec    0    621 KBytes
[  5]   4.00-5.00   sec   109 MBytes   917 Mbits/sec    0    621 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-5.00   sec   549 MBytes   921 Mbits/sec    0             sender
[  5]   0.00-5.00   sec   547 MBytes   916 Mbits/sec                  receiver

iperf Done.

Very interesting, is CPU0 slower than CPU23 by 30%?

-- 
Best Regards,
Mike Gavrilov.