[PATCH_v2] use CLOCK_MONOTONIC_COARSE posix timer instead of CLOCK_MONOTONIC in Xorg

[Daniel Stone]

On Fri, Aug 27, 2010 at 05:32:55PM +0800, ykzhao wrote:
> On Fri, 2010-08-27 at 10:15 +0800, Daniel Stone wrote:
> > On Fri, Aug 27, 2010 at 09:20:59AM +0800, yakui.zhao at intel.com wrote:
> > >    Limit the CLOCK_MONOTONIC_COARSE posix timer to linux platform. This is
> > > to avoid the issue that OS doesn't support CLOCK_MONOTINC_COARSE posix timer
> > > while the corresponding clock id is for other purpose. At the same time it
> > > won't be created if the CLOCK_MONOTONIC_COARSE is defined in system header
> > > file.
> > 
> > ... what?? CLOCK_MONOTONIC_COARSE _always_ means the coarse monotonic
> > clock if defined, on any platform.  It's always safe to use.
> 
> Do you mean that it is safe to use the coarse monotonic clock if it is
> defined? Right?

Yes.

> But in the discussion of V1 version, it seems that it is not reasonable
> for other OS. Maybe the CLOCK_MONOTONIC_COARSE posix timer is not
> supported. But the corresponding clock id is used for other purpose. In
> such case it will be not safe.

I don't think the point's getting across, and for a patch that reduces
the CPU load _less than the measurement error_, it doesn't really seem
worth discussing more.  Can you please test the attached patch and give
your Tested-by/Reviewed-by if OK? I'd like to end these threads after,
what, 60 mails? More?

Cheers,
Daniel

From 2ba33ed4671f9034172358ddc8d432b0f1730c85 Mon Sep 17 00:00:00 2001
From: Daniel Stone <daniel at fooishbar.org>
Date: Fri, 27 Aug 2010 20:36:37 +1000
Subject: [PATCH] GetTimeInMillis: Use CLOCK_MONOTONIC_COARSE where available

On some systems, using CLOCK_MONOTONIC forces a readback of HPET or some
similarly expensive timer.  CLOCK_MONOTONIC_COARSE can alleviate this,
at the cost of negligibly-reduced resolution, so prefer that where we
can.

Signed-off-by: Daniel Stone <daniel at fooishbar.org>
---
 os/utils.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/os/utils.c b/os/utils.c
index 7aa392a..efca6b4 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -429,7 +429,21 @@ GetTimeInMillis(void)
 
 #ifdef MONOTONIC_CLOCK
     struct timespec tp;
-    if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+    static clockid_t clockid;
+    if (!clockid) {
+#ifdef CLOCK_MONOTONIC_COARSE
+        if (clock_getres(CLOCK_MONOTONIC_COARSE, &tp) == 0 &&
+            (tp.tv_nsec / 1000) <= 1000 &&
+            clock_gettime(CLOCK_MONOTONIC_COARSE, &tp) == 0)
+            clockid = CLOCK_MONOTONIC_COARSE;
+        else
+#endif
+        if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+            clockid = CLOCK_MONOTONIC;
+        else
+            clockid = ~0L;
+    }
+    if (clockid != ~0L && clock_gettime(clockid, &tp) == 0)
         return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000L);
 #endif
 
-- 
1.7.1

-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://lists.x.org/archives/xorg-devel/attachments/20100827/2476d491/attachment.pgp>