linux-kernel - Re: [PATCH] net: stmmac: protect statistics updates with a spinlock

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Date: Fri, 5 Jan 2024 18:36:45 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Petr Tesařík <petr@...arici.cz>
Cc: Eric Dumazet <edumazet@...gle.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Jose Abreu <joabreu@...opsys.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>,
	"open list:STMMAC ETHERNET DRIVER" <netdev@...r.kernel.org>,
	"moderated list:ARM/STM32 ARCHITECTURE" <linux-stm32@...md-mailman.stormreply.com>,
	"moderated list:ARM/STM32 ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:ARM/Allwinner sunXi SoC support" <linux-sunxi@...ts.linux.dev>,
	Jiri Pirko <jiri@...nulli.us>
Subject: Re: [PATCH] net: stmmac: protect statistics updates with a spinlock

> This only leaves an atomic_t in hard irq context. I have tried to find
> something that could relax the requirement, but AFAICS at least some
> setups use several interrupts that can be delivered to different CPUs
> simultaneously, and all of them will walk over all channels. So we're
> left with an atomic_t here.

You might want to consider per CPU statistics. Since each CPU has its
own structure of statistics, you don't need atomic.

The code actually using the statistics then needs to sum up the per
CPU statistics, and using syncp should be sufficient for that.

Maybe look at mvneta.c for inspiration.

      Andrew