Subject: Re: [PATCH] poll/select: prevent busy-waiting

From: Johannes Sixt <[email-masked]>
Date: Mon, 28 Apr 2014 17:05:47 +0200

Am 4/28/2014 13:44, schrieb Erik Faye-Lund:
> On Mon, Apr 28, 2014 at 1:42 PM, Stepan Kasal <[email-masked]> wrote:
>> From: Paolo Bonzini <[email-masked]>
>> Date: Mon, 21 May 2012 09:52:42 +0200
>>
>> Backported from Gnulib.
>>
>> 2012-05-21  Paolo Bonzini  <[email-masked]>
>>
>>         poll/select: prevent busy-waiting.  SwitchToThread() only gives away
>>         the rest of the current time slice to another thread in the current
>>         process. So if the thread that feeds the file decscriptor we're
>>         polling is not in the current process, we get busy-waiting.
>>         * lib/poll.c: Use SleepEx(1, TRUE) instead of SwitchToThread().
>>         Patch from Theodore Leblond.
>>         * lib/select.c: Split polling out of the loop that sets the output
>>         fd_sets.  Check for zero result and loop if the wait timeout is
>>         infinite.
>>
>> Signed-off-by: Stepan Kasal <[email-masked]>
>> ---
>>  compat/poll/poll.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/compat/poll/poll.c b/compat/poll/poll.c
>> index 31163f2..a9b41d8 100644
>> --- a/compat/poll/poll.c
>> +++ b/compat/poll/poll.c
>> @@ -605,7 +605,7 @@ restart:
>>
>>    if (!rc && timeout == INFTIM)
>>      {
>> -      SwitchToThread();
>> +      SleepEx (1, TRUE);
>>        goto restart;
>>      }
>>
>> --
>> 1.9.2.msysgit.0.158.g6070cee
>>
> 
> Thanks for taking the effort!
> 
> Acked-by: Erik Faye-Lund <[email-masked]>

The patch text has my ACK, too (I've been using it since 2 years now), but
I very much prefer the commit message of the earlier post. GNU standards
w.r.t. commit messages are simply sub-par. ;-)

-- Hannes