From: Anton Blanchard Date: Wed, 10 Feb 2010 00:57:28 +0000 (+0000) Subject: powerpc: Use lwarx hint in spinlocks X-Git-Tag: v2.6.34-rc1~271^2~40 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4e14a4d17a8cd66ccab180d32c977091922cfbed;p=pandora-kernel.git powerpc: Use lwarx hint in spinlocks Recent versions of the PowerPC architecture added a hint bit to the larx instructions to differentiate between an atomic operation and a lock operation: > 0 Other programs might attempt to modify the word in storage addressed by EA > even if the subsequent Store Conditional succeeds. > > 1 Other programs will not attempt to modify the word in storage addressed by > EA until the program that has acquired the lock performs a subsequent store > releasing the lock. To avoid a binutils dependency this patch create macros for the extended lwarx format and uses it in the spinlock code. To test this change I used a simple test case that acquires and releases a global pthread mutex: pthread_mutex_lock(&mutex); pthread_mutex_unlock(&mutex); On a 32 core POWER6, running 32 test threads we spend almost all our time in the futex spinlock code: 94.37% perf [kernel] [k] ._raw_spin_lock | |--99.95%-- ._raw_spin_lock | | | |--63.29%-- .futex_wake | | | |--36.64%-- .futex_wait_setup Which is a good test for this patch. The results (in lock/unlock operations per second) are: before: 1538203 ops/sec after: 2189219 ops/sec An improvement of 42% A 32 core POWER7 improves even more: before: 1279529 ops/sec after: 2282076 ops/sec An improvement of 78% Signed-off-by: Anton Blanchard Signed-off-by: Benjamin Herrenschmidt --- Reading git-diff-tree failed