From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Carlos O'Donell <carlos@redhat.com>,
Joseph Myers <joseph@codesourcery.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
libc-alpha@sourceware.org,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Thomas Gleixner <tglx@linutronix.de>, Ben Maurer <bmaurer@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Boqun Feng <boqun.feng@gmail.com>,
Will Deacon <will.deacon@arm.com>, Paul Turner <pjt@google.com>,
linux-kernel@vger.kernel.org, linux-api@vger.kernel.org
Subject: [PATCH glibc 2/3] Linux: Use rseq in sched_getcpu if available (v9)
Date: Wed, 27 May 2020 14:51:29 -0400 [thread overview]
Message-ID: <20200527185130.5604-3-mathieu.desnoyers@efficios.com> (raw)
In-Reply-To: <20200527185130.5604-1-mathieu.desnoyers@efficios.com>
When available, use the cpu_id field from __rseq_abi on Linux to
implement sched_getcpu(). Fall-back on the vgetcpu vDSO if unavailable.
Benchmarks:
x86-64: Intel E5-2630 v3@2.40GHz, 16-core, hyperthreading
glibc sched_getcpu(): 13.7 ns (baseline)
glibc sched_getcpu() using rseq: 2.5 ns (speedup: 5.5x)
inline load cpuid from __rseq_abi TLS: 0.8 ns (speedup: 17.1x)
CC: Carlos O'Donell <carlos@redhat.com>
CC: Florian Weimer <fweimer@redhat.com>
CC: Joseph Myers <joseph@codesourcery.com>
CC: Szabolcs Nagy <szabolcs.nagy@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ben Maurer <bmaurer@fb.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Will Deacon <will.deacon@arm.com>
CC: Paul Turner <pjt@google.com>
CC: libc-alpha@sourceware.org
CC: linux-kernel@vger.kernel.org
CC: linux-api@vger.kernel.org
---
Changes since v1:
- rseq is only used if both __NR_rseq and RSEQ_SIG are defined.
Changes since v2:
- remove duplicated __rseq_abi extern declaration.
Changes since v3:
- update ChangeLog.
Changes since v4:
- Use atomic_load_relaxed to load the __rseq_abi.cpu_id field, a
consequence of the fact that __rseq_abi is not volatile anymore.
- Include atomic.h which provides atomic_load_relaxed.
Changes since v5:
- Use __ASSUME_RSEQ to detect rseq availability.
Changes since v6:
- Remove use of __ASSUME_RSEQ.
Changes since v7:
- Fix incorrect merge with commit d0def09ff6 ("linux: Fix vDSO macros
build with time64 interfaces")
Changes since v8:
- Update patch title.
- Add /* RSEQ_SIG */ for #else and #endif.
---
sysdeps/unix/sysv/linux/sched_getcpu.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
index c019cfb3cf..c0f992e056 100644
--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
@@ -18,10 +18,12 @@
#include <errno.h>
#include <sched.h>
#include <sysdep.h>
+#include <atomic.h>
#include <sysdep-vdso.h>
+#include <sys/rseq.h>
-int
-sched_getcpu (void)
+static int
+vsyscall_sched_getcpu (void)
{
unsigned int cpu;
int r = -1;
@@ -32,3 +34,19 @@ sched_getcpu (void)
#endif
return r == -1 ? r : cpu;
}
+
+#ifdef RSEQ_SIG
+int
+sched_getcpu (void)
+{
+ int cpu_id = atomic_load_relaxed (&__rseq_abi.cpu_id);
+
+ return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu ();
+}
+#else /* RSEQ_SIG */
+int
+sched_getcpu (void)
+{
+ return vsyscall_sched_getcpu ();
+}
+#endif /* RSEQ_SIG */
--
2.17.1
prev parent reply other threads:[~2020-05-27 18:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200527185130.5604-1-mathieu.desnoyers@efficios.com>
2020-05-27 18:51 ` [PATCH glibc 1/3] glibc: Perform rseq registration at C startup and thread creation (v20) Mathieu Desnoyers
2020-06-03 12:05 ` Florian Weimer
2020-06-03 12:22 ` Mathieu Desnoyers
2020-06-03 12:31 ` Florian Weimer
2020-06-03 12:40 ` Mathieu Desnoyers
2020-06-03 17:22 ` Joseph Myers
2020-06-04 11:10 ` Mathieu Desnoyers
2020-06-04 17:46 ` Joseph Myers
2020-06-11 17:47 ` Mathieu Desnoyers
2020-06-11 20:26 ` Joseph Myers
2020-06-18 12:22 ` Szabolcs Nagy
2020-06-18 13:03 ` Mathieu Desnoyers
2020-06-22 15:33 ` Mathieu Desnoyers
2020-05-27 18:51 ` Mathieu Desnoyers [this message]
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