Messages in this thread | | | Date | Tue, 4 Jul 2006 11:05:22 +0200 (MEST) | From | Mikael Pettersson <> | Subject | Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap in ctxsw |
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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). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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