From patchwork Mon Jul 2 08:27:26 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kemi Wang X-Patchwork-Id: 28189 Received: (qmail 22052 invoked by alias); 2 Jul 2018 08:31:22 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 19022 invoked by uid 89); 2 Jul 2018 08:30:28 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-25.0 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_ASCII_DIVIDERS, SPF_PASS autolearn=ham version=3.3.2 spammy=winner, Head, 0.7, blocking X-HELO: mga01.intel.com From: Kemi Wang To: Adhemerval Zanella , Florian Weimer , Rical Jason , Carlos Donell , Glibc alpha Cc: Dave Hansen , Tim Chen , Andi Kleen , Ying Huang , Aaron Lu , Lu Aubrey , Kemi Wang Subject: [PATCH v6 3/3] Mutex: Replace trylock by read only while spinning Date: Mon, 2 Jul 2018 16:27:26 +0800 Message-Id: <1530520046-18343-3-git-send-email-kemi.wang@intel.com> In-Reply-To: <1530520046-18343-1-git-send-email-kemi.wang@intel.com> References: <1530520046-18343-1-git-send-email-kemi.wang@intel.com> The pthread adaptive spin mutex spins on the lock for a while before calling into the kernel to block. But, in the current implementation of spinning, the spinners go straight back to LLL_MUTEX_TRYLOCK(cmpxchg) when the lock is contended, it is not a good idea on many targets as that will force expensive memory synchronization among processors and penalize other running threads. For example, it constantly floods the system with "read for ownership" requests, which are much more expensive to process than a single read. Thus, we only use MO read until we observe the lock to not be acquired anymore, as suggested by Andi Kleen. Performance impact: Significant mutex performance improvement is not expected for this patch, though, it probably bring some benefit for the scenarios with severe lock contention on many architectures, the whole system performance can benefit from this modification because a number of unnecessary "read for ownership" requests which stress the cache system by broadcasting cache line invalidity are eliminated during spinning. Meanwhile, it may have some tiny performance regression on the lock holder transformation for the case of lock acquisition via spinning gets, because the lock state is checked before acquiring the lock via trylock. Similar mechanism has been implemented for pthread spin lock. Test machine: 2-sockets Skylake platform, 112 cores with 62G RAM Test case: mutex-adaptive-thread (Contended pthread adaptive spin mutex with global update) Usage: make bench BENCHSET=mutex-adaptive-thread Test result: +----------------+-----------------+-----------------+------------+ | Configuration | Base | Head | % Change | | | Total iteration | Total iteration | base->head | +----------------+-----------------+-----------------+------------+ | | Critical section size: 1x | +----------------+------------------------------------------------+ |1 thread | 2.76681e+07 | 2.7965e+07 | +1.1% | |2 threads | 3.29905e+07 | 3.55279e+07 | +7.7% | |3 threads | 4.38102e+07 | 3.98567e+07 | -9.0% | |4 threads | 1.72172e+07 | 2.09498e+07 | +21.7% | |28 threads | 1.03732e+07 | 1.05133e+07 | +1.4% | |56 threads | 1.06308e+07 | 5.06522e+07 | +14.6% | |112 threads | 8.55177e+06 | 1.02954e+07 | +20.4% | +----------------+------------------------------------------------+ | | Critical section size: 10x | +----------------+------------------------------------------------+ |1 thread | 1.57006e+07 | 1.54727e+07 | -1.5% | |2 threads | 1.8044e+07 | 1.75601e+07 | -2.7% | |3 threads | 1.35634e+07 | 1.46384e+07 | +7.9% | |4 threads | 1.21257e+07 | 1.32046e+07 | +8.9% | |28 threads | 8.09593e+06 | 1.02713e+07 | +26.9% | |56 threads | 9.09907e+06 | 4.16203e+07 | +16.4% | |112 threads | 7.09731e+06 | 8.62406e+06 | +21.5% | +----------------+------------------------------------------------+ | | Critical section size: 100x | +----------------+------------------------------------------------+ |1 thread | 2.87116e+06 | 2.89188e+06 | +0.7% | |2 threads | 2.23409e+06 | 2.24216e+06 | +0.4% | |3 threads | 2.29888e+06 | 2.29964e+06 | +0.0% | |4 threads | 2.26898e+06 | 2.21394e+06 | -2.4% | |28 threads | 1.03228e+06 | 1.0051e+06 | -2.6% | |56 threads | 1.02953 +06 | 1.6344e+07 | -2.3% | |112 threads | 1.01615e+06 | 1.00134e+06 | -1.5% | +----------------+------------------------------------------------+ | | Critical section size: 1000x | +----------------+------------------------------------------------+ |1 thread | 316392 | 315635 | -0.2% | |2 threads | 302806 | 303469 | +0.2% | |3 threads | 298506 | 294281 | -1.4% | |4 threads | 292037 | 289945 | -0.7% | |28 threads | 155188 | 155250 | +0.0% | |56 threads | 190657 | 183106 | -4.0% | |112 threads | 210818 | 220342 | +4.5% | +----------------+-----------------+-----------------+------------+ * nptl/pthread_mutex_lock.c: Optimize adaptive spin mutex * nptl/pthread_mutex_timedlock.c: Likewise * sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c: Enable read only while spinning for x86 architecture * sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c: Likewise * sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c: Likewise ChangLog: V5->V6: no change V4->V5: a) Make the optimization work for pthread mutex_timedlock() in x86 architecture. b) Move the READ_ONLY_SPIN macro definition from this patch to the first patch which adds glibc.mutex.spin_count tunable entry V3->V4: a) Make the optimization opt-in, and enable for x86 architecture as default, as suggested by Florian Weimer. V2->V3: a) Drop the idea of blocking spinners if fail to acquire a lock, since this idea would not be an universal winner. E.g. several threads contend for a lock which protects a small critical section, thus, probably any thread can acquire the lock via spinning. b) Fix the format issue AFAIC V1->V2: fix format issue Suggested-by: Andi Kleen Signed-off-by: Kemi Wang --- nptl/pthread_mutex_lock.c | 15 +++++++++++++++ nptl/pthread_mutex_timedlock.c | 15 +++++++++++++++ sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c | 1 + sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c | 1 + sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c | 1 + 5 files changed, 33 insertions(+) diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c index 1519c14..9a7b5c2 100644 --- a/nptl/pthread_mutex_lock.c +++ b/nptl/pthread_mutex_lock.c @@ -124,8 +124,14 @@ __pthread_mutex_lock (pthread_mutex_t *mutex) if (LLL_MUTEX_TRYLOCK (mutex) != 0) { int cnt = 0; +#ifdef READ_ONLY_SPIN + int val = 0; + int max_cnt = MIN (__mutex_aconf.spin_count, + mutex->__data.__spins * 2 + 10); +#else int max_cnt = MIN (MAX_ADAPTIVE_COUNT, mutex->__data.__spins * 2 + 10); +#endif do { if (cnt++ >= max_cnt) @@ -133,7 +139,16 @@ __pthread_mutex_lock (pthread_mutex_t *mutex) LLL_MUTEX_LOCK (mutex); break; } +#ifdef READ_ONLY_SPIN + do + { + atomic_spin_nop (); + val = atomic_load_relaxed (&mutex->__data.__lock); + } + while (val != 0 && ++cnt < max_cnt); +#else atomic_spin_nop (); +#endif } while (LLL_MUTEX_TRYLOCK (mutex) != 0); diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c index 66efd39..dcaeca8 100644 --- a/nptl/pthread_mutex_timedlock.c +++ b/nptl/pthread_mutex_timedlock.c @@ -116,8 +116,14 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex, if (lll_trylock (mutex->__data.__lock) != 0) { int cnt = 0; +#ifdef READ_ONLY_SPIN + int val = 0; + int max_cnt = MIN (__mutex_aconf.spin_count, + mutex->__data.__spins * 2 + 10); +#else int max_cnt = MIN (MAX_ADAPTIVE_COUNT, mutex->__data.__spins * 2 + 10); +#endif do { if (cnt++ >= max_cnt) @@ -126,7 +132,16 @@ __pthread_mutex_timedlock (pthread_mutex_t *mutex, PTHREAD_MUTEX_PSHARED (mutex)); break; } +#ifdef READ_ONLY_SPIN + do + { + atomic_spin_nop (); + val = atomic_load_relaxed (&mutex->__data.__lock); + } + while (val != 0 && ++cnt < max_cnt); +#else atomic_spin_nop (); +#endif } while (lll_trylock (mutex->__data.__lock) != 0); diff --git a/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c b/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c index 967d007..a44c48c 100644 --- a/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c +++ b/sysdeps/unix/sysv/linux/x86/pthread_mutex_cond_lock.c @@ -19,4 +19,5 @@ already elided locks. */ #include +#include #include diff --git a/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c b/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c index c23678f..29d20e8 100644 --- a/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c +++ b/sysdeps/unix/sysv/linux/x86/pthread_mutex_lock.c @@ -19,4 +19,5 @@ #include #include "force-elision.h" +#include "nptl/pthread_mutex_conf.h" #include "nptl/pthread_mutex_lock.c" diff --git a/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c b/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c index 7997580..52345f5 100644 --- a/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c +++ b/sysdeps/unix/sysv/linux/x86/pthread_mutex_timedlock.c @@ -19,4 +19,5 @@ #include #include "force-elision.h" +#include "nptl/pthread_mutex_conf.h" #include "nptl/pthread_mutex_timedlock.c"