On Tue, 4 Jul 2006 01:14:13 -0700, Stephane Eranian wrote:
>On Tue, Jul 04, 2006 at 09:51:49AM +0200, Arjan van de Ven wrote:
>> > - }
>> > - }
>> > + if (unlikely((task_thread_info(next_p)->flags & _TIF_WORK_CTXSW))
>> > + || test_tsk_thread_flag(prev_p, TIF_IO_BITMAP))
>> > + __switch_to_xtra(prev_p, next_p, tss);
>>
>> well isn't this replacing an if() (which isn't cheap but also not
>> expensive, due to unlikely()) with an atomic operation (which *is*
>> expensive) ?
>>
>Andi is right. I double checked the test_tsk_thread_flag() and it does not
>use atomic ops.
The test_tsk_thread_flag() does not, but what about all the
other places in the patch where currently unsychronised loads
or stores of ->io_bitmap_ptr or ->debugreg7 get replaced or
extended with locked-on-SMP {set,clear}_{tsk_,}thread_flag()
operations?
They should all just be plain C bitops (&, |, ^, etc).
-
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