From: David Sterba <dsterba@suse.cz>
To: Nikolay Borisov <nborisov@suse.com>
Cc: Schspa Shi <schspa@gmail.com>,
clm@fb.com, dsterba@suse.com, josef@toxicpanda.com,
linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
terrelln@fb.com
Subject: Re: [PATCH v2] btrfs: zstd: use spin_lock in timer callback
Date: Wed, 13 Apr 2022 18:00:47 +0200 [thread overview]
Message-ID: <20220413160047.GL15609@suse.cz> (raw)
In-Reply-To: <09c2a9ce-3b04-ed94-1d62-0e5a072b9dac@suse.com>
On Wed, Apr 13, 2022 at 05:58:41PM +0300, Nikolay Borisov wrote:
>
>
> On 11.04.22 г. 18:55 ч., Schspa Shi wrote:
> > This is an optimization for fix fee13fe96529 ("btrfs:
> > correct zstd workspace manager lock to use spin_lock_bh()")
> >
> > The critical region for wsm.lock is only accessed by the process context and
> > the softirq context.
> >
> > Because in the soft interrupt, the critical section will not be preempted by the
> > soft interrupt again, there is no need to call spin_lock_bh(&wsm.lock) to turn
> > off the soft interrupt, spin_lock(&wsm.lock) is enough for this situation.
> >
> > Changelog:
> > v1 -> v2:
> > - Change the commit message to make it more readable.
> >
> > [1] https://lore.kernel.org/all/20220408181523.92322-1-schspa@gmail.com/
> >
> > Signed-off-by: Schspa Shi <schspa@gmail.com>
>
> Has there been any measurable impact by this change? While it's correct it does mean that
> someone looking at the code would see that in one call site we use plain spinlock and in
> another a _bh version and this is somewhat inconsistent.
I think it would be hard to measure the impact, maybe in some kind of
load the _bh version would be unnecessarily blocking some other threads.
Regarding the used locking primitives, I'll add a comment about that to
the function, it is indeed inconsistent and not obvious from the
context.
next prev parent reply other threads:[~2022-04-13 16:05 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-08 18:15 [PATCH] btrfs: zstd: use spin_lock in timer function Schspa Shi
2022-04-08 18:44 ` David Sterba
2022-04-09 7:36 ` Schspa Shi
2022-04-11 13:51 ` David Sterba
2022-04-11 15:55 ` [PATCH v2] btrfs: zstd: use spin_lock in timer callback Schspa Shi
2022-04-13 14:58 ` Nikolay Borisov
2022-04-13 16:00 ` David Sterba [this message]
2022-04-13 16:03 ` Schspa Shi
2022-04-13 19:08 ` Nikolay Borisov
2022-04-14 16:39 ` Schspa Shi
2022-04-14 19:26 ` David Sterba
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