From: Anand Jain <anand.jain@oracle.com>
To: dsterba@suse.cz
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 4/4] btrfs: use test_and_clear_bit() in wait_dev_flush()
Date: Tue, 28 Mar 2023 13:05:12 +0800 [thread overview]
Message-ID: <4eba5d17-ba03-46b6-a936-1d9a9bc55960@oracle.com> (raw)
In-Reply-To: <20230327171427.GI10580@twin.jikos.cz>
On 3/28/23 01:14, David Sterba wrote:
> On Mon, Mar 27, 2023 at 05:53:10PM +0800, Anand Jain wrote:
>> The function wait_dev_flush() tests for the BTRFS_DEV_STATE_FLUSH_SENT
>> bit and then clears it separately. Instead, use test_and_clear_bit().
>
> But why would we need to do it like that? The write and wait are
> executed in one thread so we don't need atomic change to the status and
> thus a separate set/test/clear bit are fine. If not, then please
> explain. Thanks.
It's true that atomic test_and_clear_bit() isn't necessary in this case.
Nonetheless, using it have benefits such as cleaner code and improved
efficiency[1].
[1]. I was curious, so I made wait_dev_flush() non-inline and checked
the ASM code for wait_dev_flush(). After the patch, there were 8 fewer
instructions.
I'm okay with dropping this patch if you prefer to maintain the correct
usage of test_and_clear_bit().
Thanks, Anand
next prev parent reply other threads:[~2023-03-28 5:05 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-27 9:53 [PATCH 0/4] btrfs: optimize disks flush code Anand Jain
2023-03-27 9:53 ` [PATCH 1/4] btrfs: move last_flush_error to write_dev_flush and wait_dev_flush Anand Jain
2023-03-27 9:53 ` [PATCH 2/4] btrfs: opencode check_barrier_error() Anand Jain
2023-03-27 9:53 ` [PATCH 3/4] Btrfs: change wait_dev_flush() return type to bool Anand Jain
2023-03-27 17:11 ` David Sterba
2023-03-28 2:58 ` Anand Jain
2023-03-27 23:52 ` kernel test robot
2023-03-28 5:31 ` [PATCH] fixup: Btrfs: change wait_dev_flush() return type to bool v2 Anand Jain
2023-03-28 18:28 ` David Sterba
2023-03-27 9:53 ` [PATCH 4/4] btrfs: use test_and_clear_bit() in wait_dev_flush() Anand Jain
2023-03-27 17:14 ` David Sterba
2023-03-28 5:05 ` Anand Jain [this message]
2023-03-28 18:33 ` David Sterba
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