GNU bug report logs - #51734
29.0.50; got slow

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From: Ken Brown <kbrown <at> cornell.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: yamaoka <at> jpl.org, 51734 <at> debbugs.gnu.org
Subject: bug#51734: 29.0.50; got slow
Date: Fri, 12 Nov 2021 13:22:28 -0500

On 11/11/2021 3:36 PM, Eli Zaretskii wrote:
> LGTM, thanks.  It would be good to understand why starting alarms
> causes slowdown on Cygwin, though.

I asked on the cygwin-developers list, and Corinna is not aware of any reason 
there should be a problem using timerfd and POSIX timers simultaneously.  [In 
case it wasn't clear, the slowdown occurs only if we use both timerfd and 
alarms; either one by itself is fine.]

The only thing I can think of is that Cygwin is probably the only system that 
has timerfd and that also has to use timers to poll for input.  (The others all 
use SIGIO, if I'm not mistaken.)  By using two different kinds of timers 
simultaneously, we're getting timers expiring twice as often and not at regular 
intervals.  Could this account for the slowdown?

In any case, I think I should go ahead and install the patch to make the master 
branch usable again on Cygwin.

Ken

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