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Revert of Use CLOCK_REALTIME_COARSE when available. (patchset #3 id:40001 of https://codereview.chromium.org/1125003002/)

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Reason for revert:
[Sheriff] This causes layout test crashes:
http://build.chromium.org/p/client.v8/builders/V8-Blink%20Linux%2064%20%28dbg%29/builds/2735

You can add the trybot v8_linux_layout_dbg on reland.

Original issue's description:
> Use CLOCK_REALTIME_COARSE when available.
>
> On systems that have CLOCK_REALTIME_COARSE with good enough resolution, we can
> avoid making a system call to get the current time; it's serviced from the vDSO.
>
> BUG=
> LOG=N
>
> Committed: https://crrev.com/537ed7500c087786f28f51ff5222f1c2113776d3
> Cr-Commit-Position: refs/heads/master@{#28280}

TBR=jochen@chromium.org,deanm@chromium.org,bmeurer@chromium.org,ben@strongloop.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1130083003

Cr-Commit-Position: refs/heads/master@{#28288}
This commit is contained in:
machenbach 2015-05-07 01:51:34 -07:00 committed by Commit bot
parent 2f9411df89
commit e137650825
1 changed files with 0 additions and 38 deletions
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38
src/base/platform/time.cc
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@ -24,11 +24,6 @@
#include "src/base/logging.h"
#include "src/base/platform/platform.h"
// CLOCK_REALTIME_COARSE was added in Linux 2.6.32.
#if V8_OS_LINUX && !defined(CLOCK_REALTIME_COARSE)
#define CLOCK_REALTIME_COARSE 5
#endif
namespace v8 {
namespace base {
@ -257,44 +252,11 @@ FILETIME Time::ToFiletime() const {
#elif V8_OS_POSIX
Time Time::Now() {
#ifdef CLOCK_REALTIME_COARSE
struct timespec ts;
// clockid_t is an int32_t; loads and stores are atomic.
static const clockid_t kInvalidClockId = static_cast<clockid_t>(-1);
static clockid_t clock_id = kInvalidClockId;
if (V8_UNLIKELY(clock_id == kInvalidClockId)) {
// CLOCK_REALTIME_COARSE is not supported on Linux kernels < 2.6.32.
// Probe the kernel to see if it's available and has <= 1 ms resolution.
//
// CLOCK_REALTIME_COARSE, unlike CLOCK_REALTIME, can often be serviced
// entirely from the vDSO without the need to make a system call.
// It can have a dramatic impact on applications that frequently
// query the current time.
//
// One caveat is that CLOCK_REALTIME_COARSE is tied to CONFIG_HZ, the
// number of ticks per second that the kernel runs at. Its granularity
// can be as low as one update every 300 ms so we need to make sure that
// it is accurate enough. Fortunately, many if not most kernels are built
// with CONFIG_HZ=1000, giving it a one millisecond precision and that is
// good enough for our purposes.
if (clock_getres(CLOCK_REALTIME_COARSE, &ts) < 0 || ts.tv_sec > 0 ||
ts.tv_nsec > 1000 * 1000) {
clock_id = CLOCK_REALTIME; // Not available or not suitable.
} else {
clock_id = CLOCK_REALTIME_COARSE;
}
}
int result = clock_gettime(clock_id, &ts);
DCHECK_EQ(0, result);
USE(result);
return FromTimespec(ts);
#else
struct timeval tv;
int result = gettimeofday(&tv, NULL);
DCHECK_EQ(0, result);
USE(result);
return FromTimeval(tv);
#endif
}