Re: The timerfd functions slow down emacs

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Feb 23 20:48, Ken Brown wrote:
> On 2/23/2019 2:15 PM, Corinna Vinschen wrote:
> > Below's the NSSTC I used to test my timerfd implementation (based on
> > another STC to show a problem in POSIX timers).  From what I can tell it
> > works as desired.  If you find a problem, please point it out or send a
> > patch.
> 
> Thanks, that saved me a lot of time.  I was in the process of creating a test 
> case when your mail arrived.
> 
> Your test works fine.  For example:
> 
> $ gcc timerfd_test.c -o timerfd_test
> 
> $ ./timerfd_test.exe 3 1 10
> 0.000: timer started 52379
> 2.988: 52379 read: 1; total=1
> 3.988: 52379 read: 1; total=2
> 4.989: 52379 read: 1; total=3
> 5.987: 52379 read: 1; total=4
> 7.001: 52379 read: 1; total=5
> 7.987: 52379 read: 1; total=6
> 9.001: 52379 read: 1; total=7
> 9.987: 52379 read: 1; total=8
> 10.987: 52379 read: 1; total=9
> 11.997: 52379 read: 1; total=10
> 
> But if I change CLOCK_MONOTONIC by CLOCK_REALTIME in the call to timerfd_create, 
> then I get the following:

Only in timerfd_create?  Not in clock_gettime?  If you don't
do that, you're using a different clock with entirely different
values for the starttime.

Actually, this testcase started with CLOCK_REALTIME in both calls.
If I revert to that, I get:

)$ ./timerfd 3 1 10
0.000: timer started 644
3.001: 644 read: 1; total=1
4.001: 644 read: 1; total=2
5.017: 644 read: 1; total=3
6.001: 644 read: 1; total=4
7.001: 644 read: 1; total=5
8.009: 644 read: 1; total=6
9.002: 644 read: 1; total=7
10.001: 644 read: 1; total=8
11.010: 644 read: 1; total=9
12.017: 644 read: 1; total=10

I tested this STC with differnt clocks, but it's important to
use the same cloack for clock_gettime and timerfd_create.


Corinna

> 
> $ ./timerfd_test.exe 3 1 10
> 0.000: timer started 52385
> 0.006: 52385 read: 1550343072; total=1550343072


> 
> In particular, 'select' returns immediately.  In the case of emacs, BTW, timerfd 
> is called like this:
> 
>    fd = timerfd_create (CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC);
> 
> Ken

-- 
Corinna Vinschen
Cygwin Maintainer

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