netdev - Re: [PATCH net] net: stmmac: Use hrtimer for TX coalescing

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Date: Mon, 18 Sep 2023 12:56:31 +0000
From: Vincent Whitchurch <Vincent.Whitchurch@...s.com>
To: "maxtram95@...il.com" <maxtram95@...il.com>, Vincent Whitchurch
	<Vincent.Whitchurch@...s.com>
CC: "davem@...emloft.net" <davem@...emloft.net>, "nbd@....name"
	<nbd@....name>, "alexandre.torgue@...com" <alexandre.torgue@...com>,
	"joabreu@...opsys.com" <joabreu@...opsys.com>, kernel <kernel@...s.com>,
	"peppe.cavallaro@...com" <peppe.cavallaro@...com>, "kuba@...nel.org"
	<kuba@...nel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] net: stmmac: Use hrtimer for TX coalescing

On Wed, 2023-08-30 at 21:05 +0300, Maxim Mikityanskiy wrote:
> On Wed, 30 Aug 2023 at 14:55:37 +0000, Vincent Whitchurch wrote:
> > Any test results with this patch on the hardware with the performance
> > problems would be appreciated.
> 
> TL/DR: it's definitely better than without the patch, but still worse
> than fully reverting hrtimer [1].

Thank you for testing this.

Have you also had the chance to try out Felix's suggestion of completely
disabling coalescing in the driver?  For that you will need to apply the
patch at [0] (the command below may appear to work without the patch but
the timer will continue to be programmed and expire immediately if the
patch is not applied) and then run something like:

  ethtool -C eth0 tx-frame 1 tx-usecs 0

[0] https://lore.kernel.org/all/20230907-stmmac-coaloff-v2-1-38ccfac548b9@axis.com/

With coalescing disabled in the driver, there is also the option of
playing with the generic software IRQ coalescing options available in
NAPI in newer kernels (eg. gro_flush_timeout), which may work better for
you than the one in the driver.