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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>
This commit is contained in:
Linus Torvalds 2008-06-22 12:23:15 -07:00
parent 481c5346d0
commit 55d8538498
1 changed files with 1 additions and 1 deletions
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2
fs/select.c
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@ -249,7 +249,6 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout)
retval++; retval++;
} }
} }
cond_resched();
} }
if (res_in) if (res_in)
*rinp = res_in; *rinp = res_in;
@ -257,6 +256,7 @@ int do_select(int n, fd_set_bits *fds, s64 *timeout)
*routp = res_out; *routp = res_out;
if (res_ex) if (res_ex)
*rexp = res_ex; *rexp = res_ex;
cond_resched();
} }
wait = NULL; wait = NULL;
if (retval || !*timeout || signal_pending(current)) if (retval || !*timeout || signal_pending(current))