Tim Chen wrote:
Hi Herbet,
The patch "Let WARN_ON/WARN_ON_ONCE return the condition"
http://kernel.org/git/?
p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=684f978347deb42d180373ac4c427f82ef963171
introduced 40% more 2nd level cache miss to tbench workload
being run in a loop back mode on a Core 2 machine. I think the
introduction of the local variables to WARN_ON and WARN_ON_ONCE
typeof(x) __ret_warn_on = (x);
typeof(condition) __ret_warn_once = (condition);
results in the extra cache misses. In our test workload profile, we see
heavily used functions like do_softirq and local_bh_enable
takes a lot longer to execute.
The modification below helps fix the problem. I made a slight
modification to sched.c to get around a gcc bug.
How does the generated code change? Doesn't evaluating the condition
multiple times have the potential to cause problems?
J
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