linux-kernel - Re: [PATCH 6/8] net: tcp: tsq: Convert from tasklet to BH workqueue

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Message-ID: <Zc7zLsEhDzGkCH9m@slm.duckdns.org>
Date: Thu, 15 Feb 2024 19:31:26 -1000
From: Tejun Heo <tj@...nel.org>
To: torvalds@...ux-foundation.org, mpatocka@...hat.com
Cc: linux-kernel@...r.kernel.org, dm-devel@...ts.linux.dev,
	msnitzer@...hat.com, ignat@...udflare.com, damien.lemoal@....com,
	bob.liu@...cle.com, houtao1@...wei.com, peterz@...radead.org,
	mingo@...nel.org, netdev@...r.kernel.org, allen.lkml@...il.com,
	kernel-team@...a.com, Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, David Wei <davidhwei@...a.com>
Subject: Re: [PATCH 6/8] net: tcp: tsq: Convert from tasklet to BH workqueue

Hello,

On Mon, Jan 29, 2024 at 11:11:53PM -1000, Tejun Heo wrote:
> The only generic interface to execute asynchronously in the BH context is
> tasklet; however, it's marked deprecated and has some design flaws. To
> replace tasklets, BH workqueue support was recently added. A BH workqueue
> behaves similarly to regular workqueues except that the queued work items
> are executed in the BH context.
> 
> This patch converts TCP Small Queues implementation from tasklet to BH
> workqueue.
> 
> Semantically, this is an equivalent conversion and there shouldn't be any
> user-visible behavior changes. While workqueue's queueing and execution
> paths are a bit heavier than tasklet's, unless the work item is being queued
> every packet, the difference hopefully shouldn't matter.
> 
> My experience with the networking stack is very limited and this patch
> definitely needs attention from someone who actually understands networking.

On Jakub's recommendation, I asked David Wei to perform production memcache
benchmark on the backported conversion patch. There was no discernible
difference before and after. Given that this is likely as hot as it gets for
the path on a real workloal, the conversions shouldn't hopefully be
noticeable in terms of performance impact.

Jakub, I'd really appreciate if you could ack. David, would it be okay if I
add your Tested-by?

Thanks.

-- 
tejun