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authorLinus Torvalds <torvalds@linux-foundation.org>2008-06-22 12:23:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-06-22 12:23:15 -0700
commit55d8538498f62ec72b5ba67aa386c7726f630475 (patch)
tree15ebcc7a51fdf1ff2bf76ade337a637c0990055d /fs/select.c
parent481c5346d0981940ee63037eb53e4e37b0735c10 (diff)
downloadlinux-55d8538498f62ec72b5ba67aa386c7726f630475.tar.gz
Fix performance regression on lmbench select benchmark
Christian Borntraeger reported that reinstating cond_resched() with CONFIG_PREEMPT caused a performance regression on lmbench: For example select file 500: 23 microseconds 32 microseconds and that's really because we totally unnecessarily do the cond_resched() in the innermost loop of select(), which is just silly. This moves it out from the innermost loop (which only ever loops ove the bits in a single "unsigned long" anyway), which makes the performance regression go away. Reported-and-tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/select.c')
-rw-r--r--fs/select.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/select.c b/fs/select.c
index 8dda969614a..da0e88201c3 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -249,7 +249,6 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout)
retval++;
}
}
- cond_resched();
}
if (res_in)
*rinp = res_in;
@@ -257,6 +256,7 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout)
*routp = res_out;
if (res_ex)
*rexp = res_ex;
+ cond_resched();
}
wait = NULL;
if (retval || !*timeout || signal_pending(current))