[2/4] glibc: sched_getcpu(): use rseq cpu_id TLS on Linux

Message ID 20190212194253.1951-3-mathieu.desnoyers@efficios.com
State Superseded
Headers show
Series
  • Restartable Sequences support for glibc 2.30
Related show

Commit Message

Mathieu Desnoyers Feb. 12, 2019, 7:42 p.m.
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)

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

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: Dave Watson <davejwatson@fb.com>
CC: Paul Turner <pjt@google.com>
CC: libc-alpha@sourceware.org
CC: linux-kernel@vger.kernel.org
CC: linux-api@vger.kernel.org
---
 sysdeps/unix/sysv/linux/sched_getcpu.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

-- 
2.17.1

Comments

Carlos O'Donell March 22, 2019, 8:13 p.m. | #1
On 2/12/19 2:42 PM, Mathieu Desnoyers wrote:
> 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


This patch looks good to me for master, but is blocked on patch 1/4
being reworked.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>


> 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)

> 

> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

> 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: Dave Watson <davejwatson@fb.com>

> CC: Paul Turner <pjt@google.com>

> CC: libc-alpha@sourceware.org

> CC: linux-kernel@vger.kernel.org

> CC: linux-api@vger.kernel.org

> ---

>   sysdeps/unix/sysv/linux/sched_getcpu.c | 25 +++++++++++++++++++++++--

>   1 file changed, 23 insertions(+), 2 deletions(-)

> 

> diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c

> index fb0d317f83..8bfb03778b 100644

> --- a/sysdeps/unix/sysv/linux/sched_getcpu.c

> +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c

> @@ -24,8 +24,8 @@

>   #endif

>   #include <sysdep-vdso.h>

>   

> -int

> -sched_getcpu (void)

> +static int

> +vsyscall_sched_getcpu (void)


OK.

>   {

>   #ifdef __NR_getcpu

>     unsigned int cpu;

> @@ -37,3 +37,24 @@ sched_getcpu (void)

>     return -1;

>   #endif

>   }

> +

> +#ifdef __NR_rseq

> +#include <linux/rseq.h>

> +

> +extern __attribute__ ((tls_model ("initial-exec")))

> +__thread volatile struct rseq __rseq_abi;


OK.

> +

> +int

> +sched_getcpu (void)

> +{

> +  int cpu_id = __rseq_abi.cpu_id;

> +

> +  return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu ();


OK. Impressive :-)

> +}

> +#else

> +int

> +sched_getcpu (void)

> +{

> +  return vsyscall_sched_getcpu ();


OK.

> +}

> +#endif

> 



-- 
Cheers,
Carlos.

Patch

diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
index fb0d317f83..8bfb03778b 100644
--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
@@ -24,8 +24,8 @@ 
 #endif
 #include <sysdep-vdso.h>
 
-int
-sched_getcpu (void)
+static int
+vsyscall_sched_getcpu (void)
 {
 #ifdef __NR_getcpu
   unsigned int cpu;
@@ -37,3 +37,24 @@  sched_getcpu (void)
   return -1;
 #endif
 }
+
+#ifdef __NR_rseq
+#include <linux/rseq.h>
+
+extern __attribute__ ((tls_model ("initial-exec")))
+__thread volatile struct rseq __rseq_abi;
+
+int
+sched_getcpu (void)
+{
+  int cpu_id = __rseq_abi.cpu_id;
+
+  return cpu_id >= 0 ? cpu_id : vsyscall_sched_getcpu ();
+}
+#else
+int
+sched_getcpu (void)
+{
+  return vsyscall_sched_getcpu ();
+}
+#endif