netdev - Re: [PATCH] drivers/net/b44: Change to non-atomic bit operations

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Date:   Tue, 24 Dec 2019 17:10:20 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     David Miller <davem@...emloft.net>
Cc:     michael.chan@...adcom.com, netdev@...r.kernel.org,
        tglx@...utronix.de, luto@...nel.org, peterz@...radead.org,
        tony.luck@...el.com, David.Laight@...LAB.COM,
        ravi.v.shankar@...el.com
Subject: Re: [PATCH] drivers/net/b44: Change to non-atomic bit operations

On Tue, Dec 24, 2019 at 04:18:26PM -0800, David Miller wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
> Date: Fri, 20 Dec 2019 15:29:11 -0800
> 
> > On x86, accessing data across two cache lines in one atomic bit
> > operation (aka split lock) can take over 1000 cycles.
> 
> This happens during configuration of WOL, nobody cares that the atomic
> operations done in this function take 1000 cycles each.
> 
> I'm not applying this patch.  It is gratuitous, and the commit message
> talks about "performance" considuations (cycle counts) that completely
> don't matter here.
> 
> If you are merely just arbitrarily trying to remove locked atomic
> operations across the tree for it's own sake, then you should be
> completely honest about that in your commit message.

We are enabling split lock in the kernel (by default):
https://lkml.org/lkml/2019/12/12/1129

After applying the split lock detection patch, the set_bit() in b44.c
may cause split lock and kernel dies.

So should I change the commit message to add the above info?

Thanks.

-Fenghua