Message ID | 20200326155633.18236-7-mathieu.desnoyers@efficios.com |
---|---|
State | New |
Headers | show |
Series | Restartable Sequences enablement | expand |
* Mathieu Desnoyers via Libc-alpha: > diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c > index c019cfb3cf..2269c4f2bd 100644 > --- a/sysdeps/unix/sysv/linux/sched_getcpu.c > +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c > @@ -18,10 +18,15 @@ > #include <errno.h> > #include <sched.h> > #include <sysdep.h> > +#include <atomic.h> > #include <sysdep-vdso.h> > > -int > -sched_getcpu (void) > +#ifdef HAVE_GETCPU_VSYSCALL > +# define HAVE_VSYSCALL > +#endif > + > +static int > +vsyscall_sched_getcpu (void) > { > unsigned int cpu; > int r = -1; > @@ -32,3 +37,21 @@ sched_getcpu (void) > #endif > return r == -1 ? r : cpu; > } > + > +#include <sys/rseq.h> > + > +#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 > +int > +sched_getcpu (void) > +{ > + return vsyscall_sched_getcpu (); > +} > +#endif This patch needs to be rebased on current master, but the direction looks right to me.
diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c index c019cfb3cf..2269c4f2bd 100644 --- a/sysdeps/unix/sysv/linux/sched_getcpu.c +++ b/sysdeps/unix/sysv/linux/sched_getcpu.c @@ -18,10 +18,15 @@ #include <errno.h> #include <sched.h> #include <sysdep.h> +#include <atomic.h> #include <sysdep-vdso.h> -int -sched_getcpu (void) +#ifdef HAVE_GETCPU_VSYSCALL +# define HAVE_VSYSCALL +#endif + +static int +vsyscall_sched_getcpu (void) { unsigned int cpu; int r = -1; @@ -32,3 +37,21 @@ sched_getcpu (void) #endif return r == -1 ? r : cpu; } + +#include <sys/rseq.h> + +#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 +int +sched_getcpu (void) +{ + return vsyscall_sched_getcpu (); +} +#endif
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: 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. --- sysdeps/unix/sysv/linux/sched_getcpu.c | 27 ++++++++++++++++++++++++-- 1 file changed, 25 insertions(+), 2 deletions(-)