• Davidlohr Bueso's avatar
    ipc,sem: do not hold ipc lock more than necessary · 16df3674
    Davidlohr Bueso authored
    Instead of holding the ipc lock for permissions and security checks, among
    others, only acquire it when necessary.
    
    Some numbers....
    
    1) With Rik's semop-multi.c microbenchmark we can see the following
       results:
    
    Baseline (3.9-rc1):
    cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
    total operations: 151452270, ops/sec 5048409
    
    +  59.40%            a.out  [kernel.kallsyms]  [k] _raw_spin_lock
    +   6.14%            a.out  [kernel.kallsyms]  [k] sys_semtimedop
    +   3.84%            a.out  [kernel.kallsyms]  [k] avc_has_perm_flags
    +   3.64%            a.out  [kernel.kallsyms]  [k] __audit_syscall_exit
    +   2.06%            a.out  [kernel.kallsyms]  [k] copy_user_enhanced_fast_string
    +   1.86%            a.out  [kernel.kallsyms]  [k] ipc_lock
    
    With this patchset:
    cpus 4, threads: 256, semaphores: 128, test duration: 30 secs
    total operations: 273156400, ops/sec 9105213
    
    +  18.54%            a.out  [kernel.kallsyms]  [k] _raw_spin_lock
    +  11.72%            a.out  [kernel.kallsyms]  [k] sys_semtimedop
    +   7.70%            a.out  [kernel.kallsyms]  [k] ipc_has_perm.isra.21
    +   6.58%            a.out  [kernel.kallsyms]  [k] avc_has_perm_flags
    +   6.54%            a.out  [kernel.kallsyms]  [k] __audit_syscall_exit
    +   4.71%            a.out  [kernel.kallsyms]  [k] ipc_obtain_object_check
    
    2) While on an Oracle swingbench DSS (data mining) workload the
       improvements are not as exciting as with Rik's benchmark, we can see
       some positive numbers.  For an 8 socket machine the following are the
       percentages of %sys time incurred in the ipc lock:
    
    Baseline (3.9-rc1):
    100 swingbench users: 8,74%
    400 swingbench users: 21,86%
    800 swingbench users: 84,35%
    
    With this patchset:
    100 swingbench users: 8,11%
    400 swingbench users: 19,93%
    800 swingbench users: 77,69%
    
    [riel@redhat.com: fix two locking bugs]
    [sasha.levin@oracle.com: prevent releasing RCU read lock twice in semctl_main]
    [akpm@linux-foundation.org: coding-style fixes]
    Signed-off-by: default avatarDavidlohr Bueso <davidlohr.bueso@hp.com>
    Signed-off-by: default avatarRik van Riel <riel@redhat.com>
    Reviewed-by: default avatarChegu Vinod <chegu_vinod@hp.com>
    Acked-by: default avatarMichel Lespinasse <walken@google.com>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Jason Low <jason.low2@hp.com>
    Cc: Emmanuel Benisty <benisty.e@gmail.com>
    Cc: Peter Hurley <peter@hurleysoftware.com>
    Cc: Stanislav Kinsbursky <skinsbursky@parallels.com>
    Tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    16df3674
sem.c 44 KB