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X-HELO: mout.kundenserver.de
Date: Sat, 23 Feb 2019 22:01:52 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: Ken Brown <kbrown AT cornell DOT edu>
Cc: "cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
Subject: Re: The timerfd functions slow down emacs
Message-ID: <20190223210152.GA4133@calimero.vinschen.de>
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Mail-Followup-To: Ken Brown <kbrown AT cornell DOT edu>,	"cygwin AT cygwin DOT com" <cygwin AT cygwin DOT com>
References: <04048cc3-091a-b55c-372b-bde29273d952 AT cornell DOT edu> <1df3d7ce-1427-cbd4-0978-7236b1903440 AT cornell DOT edu> <20190223191542 DOT GS4256 AT calimero DOT vinschen DOT de> <0f2789ab-5722-c0de-6176-d4e1aaff9f81 AT cornell DOT edu>
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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.
>=20
> Thanks, that saved me a lot of time.  I was in the process of creating a =
test=20
> case when your mail arrived.
>=20
> Your test works fine.  For example:
>=20
> $ gcc timerfd_test.c -o timerfd_test
>=20
> $ ./timerfd_test.exe 3 1 10
> 0.000: timer started 52379
> 2.988: 52379 read: 1; total=3D1
> 3.988: 52379 read: 1; total=3D2
> 4.989: 52379 read: 1; total=3D3
> 5.987: 52379 read: 1; total=3D4
> 7.001: 52379 read: 1; total=3D5
> 7.987: 52379 read: 1; total=3D6
> 9.001: 52379 read: 1; total=3D7
> 9.987: 52379 read: 1; total=3D8
> 10.987: 52379 read: 1; total=3D9
> 11.997: 52379 read: 1; total=3D10
>=20
> But if I change CLOCK_MONOTONIC by CLOCK_REALTIME in the call to timerfd_=
create,=20
> 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=3D1
4.001: 644 read: 1; total=3D2
5.017: 644 read: 1; total=3D3
6.001: 644 read: 1; total=3D4
7.001: 644 read: 1; total=3D5
8.009: 644 read: 1; total=3D6
9.002: 644 read: 1; total=3D7
10.001: 644 read: 1; total=3D8
11.010: 644 read: 1; total=3D9
12.017: 644 read: 1; total=3D10

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


Corinna

>=20
> $ ./timerfd_test.exe 3 1 10
> 0.000: timer started 52385
> 0.006: 52385 read: 1550343072; total=3D1550343072


>=20
> In particular, 'select' returns immediately.  In the case of emacs, BTW, =
timerfd=20
> is called like this:
>=20
>    fd =3D timerfd_create (CLOCK_REALTIME, TFD_NONBLOCK | TFD_CLOEXEC);
>=20
> Ken

--=20
Corinna Vinschen
Cygwin Maintainer

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