• Pan Xinhui's avatar
    locking/mutex: Break out of expensive busy-loop on... · 05ffc951
    Pan Xinhui authored
    locking/mutex: Break out of expensive busy-loop on {mutex,rwsem}_spin_on_owner() when owner vCPU is preempted
    
    An over-committed guest with more vCPUs than pCPUs has a heavy overload
    in the two spin_on_owner. This blames on the lock holder preemption
    issue.
    
    Break out of the loop if the vCPU is preempted: if vcpu_is_preempted(cpu)
    is true.
    
    test-case:
    perf record -a perf bench sched messaging -g 400 -p && perf report
    
    before patch:
    20.68%  sched-messaging  [kernel.vmlinux]  [k] mutex_spin_on_owner
     8.45%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
     4.12%  sched-messaging  [kernel.vmlinux]  [k] system_call
     3.01%  sched-messaging  [kernel.vmlinux]  [k] system_call_common
     2.83%  sched-messaging  [kernel.vmlinux]  [k] copypage_power7
     2.64%  sched-messaging  [kernel.vmlinux]  [k] rwsem_spin_on_owner
     2.00%  sched-messaging  [kernel.vmlinux]  [k] osq_lock
    
    after patch:
     9.99%  sched-messaging  [kernel.vmlinux]  [k] mutex_unlock
     5.28%  sched-messaging  [unknown]         [H] 0xc0000000000768e0
     4.27%  sched-messaging  [kernel.vmlinux]  [k] __copy_tofrom_user_power7
     3.77%  sched-messaging  [kernel.vmlinux]  [k] copypage_power7
     3.24%  sched-messaging  [kernel.vmlinux]  [k] _raw_write_lock_irq
     3.02%  sched-messaging  [kernel.vmlinux]  [k] system_call
     2.69%  sched-messaging  [kernel.vmlinux]  [k] wait_consider_task
    Tested-by: default avatarJuergen Gross <jgross@suse.com>
    Signed-off-by: default avatarPan Xinhui <xinhui.pan@linux.vnet.ibm.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Acked-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
    Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    Cc: David.Laight@ACULAB.COM
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: benh@kernel.crashing.org
    Cc: boqun.feng@gmail.com
    Cc: bsingharora@gmail.com
    Cc: dave@stgolabs.net
    Cc: kernellwp@gmail.com
    Cc: konrad.wilk@oracle.com
    Cc: linuxppc-dev@lists.ozlabs.org
    Cc: mpe@ellerman.id.au
    Cc: paulmck@linux.vnet.ibm.com
    Cc: paulus@samba.org
    Cc: rkrcmar@redhat.com
    Cc: virtualization@lists.linux-foundation.org
    Cc: will.deacon@arm.com
    Cc: xen-devel-request@lists.xenproject.org
    Cc: xen-devel@lists.xenproject.org
    Link: http://lkml.kernel.org/r/1478077718-37424-4-git-send-email-xinhui.pan@linux.vnet.ibm.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    05ffc951
rwsem-xadd.c 18 KB