From: Eric Dumazet <eric.dumazet@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>,
xiaolinkui <xiaolinkui@kylinos.cn>
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: Re: [PATCH] net: use unlikely for dql_avail case
Date: Thu, 26 Sep 2019 15:52:29 -0700 [thread overview]
Message-ID: <d5225e3a-717e-c836-f94c-6df4f29e43ca@gmail.com> (raw)
In-Reply-To: <20190925122501.GA27720@pc-66.home>
On 9/25/19 5:25 AM, Daniel Borkmann wrote:
> On Wed, Sep 25, 2019 at 10:40:43AM +0800, xiaolinkui wrote:
>> This is an unlikely case, use unlikely() on it seems logical.
>>
>> Signed-off-by: xiaolinkui <xiaolinkui@kylinos.cn>
>
> It's already here [0], but should probably rather get reverted instead
> due to lack of a more elaborate reasoning on why it needs to be done
> this way instead of letting compiler do it's job in this case. "Seems
> logical" is never a good technical explanation. Do you have any better
> analysis you performed prior to submitting the patch (twice by now)?
>
Yes, we need more details here.
We could probably save more cpu cycles checking if we can move
the smb_mb() after the dql_avail() check :)
> Thanks,
> Daniel
>
> [0] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=f3acd33d840d3ea3e1233d234605c85cbbf26054
>
>> ---
>> include/linux/netdevice.h | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index 88292953aa6f..005f3da1b13d 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -3270,7 +3270,7 @@ static inline void netdev_tx_completed_queue(struct netdev_queue *dev_queue,
>> */
>> smp_mb();
>>
>> - if (dql_avail(&dev_queue->dql) < 0)
>> + if (unlikely(dql_avail(&dev_queue->dql) < 0))
>> return;
>>
>> if (test_and_clear_bit(__QUEUE_STATE_STACK_XOFF, &dev_queue->state))
>> --
>> 2.17.1
>>
>>
>>
next prev parent reply other threads:[~2019-09-26 22:52 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 2:40 [PATCH] net: use unlikely for dql_avail case xiaolinkui
2019-09-25 12:25 ` Daniel Borkmann
2019-09-26 22:52 ` Eric Dumazet [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-08-22 6:58 xiaolinkui
2019-08-24 21:23 ` David Miller
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