linux-kernel - Re: [PATCH net-next] qlcnic: Optimize performance by replacing rw

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Message-ID: <Z8xx0aN4vA7d-73i@eleanor-wkdl>
Date: Sun, 9 Mar 2025 00:35:29 +0800
From: Yu-Chun Lin <eleanor15x@...il.com>
To: Simon Horman <horms@...nel.org>
Cc: shshaikh@...vell.com, manishc@...vell.com, GR-Linux-NIC-Dev@...vell.com,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, jserv@...s.ncku.edu.tw,
	visitorckw@...il.com
Subject: Re: [PATCH net-next] qlcnic: Optimize performance by replacing
 rw_lock with spinlock

On Fri, Mar 07, 2025 at 01:29:29PM +0000, Simon Horman wrote:
> On Fri, Mar 07, 2025 at 12:31:24AM +0800, Yu-Chun Lin wrote:
> > The 'crb_lock', an rwlock, is only used by writers, making it functionally
> > equivalent to a spinlock.
> > 
> > According to Documentation/locking/spinlocks.rst:
> > 
> > "Reader-writer locks require more atomic memory operations than simple
> > spinlocks. Unless the reader critical section is long, you are better
> > off just using spinlocks."
> > 
> > Since read_lock() is never called, switching to a spinlock reduces
> > overhead and improves efficiency.
> > 
> > Signed-off-by: Yu-Chun Lin <eleanor15x@...il.com>
> 
> Hi Yu-Chun Lin,
> 
> Thanks for your patch.
> 
> My main question is if you have hardware to test this?
> And if so, was a benefit observed?
> 
> If not, my feeling is that although your change looks
> correct, we'd be better off taking the lower risk option
> of leaving things be.

Hi Simon

I perform a compile test to ensure correctness. But I don't have the
hardware to run a full test.

Yu-Chun Lin