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.z...@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 <dan...@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 <dan...@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
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