Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [PATCH 1/2] x86-64 TIF flags for debug regs and io bitmap in ctxsw | Date | Tue, 4 Jul 2006 12:22:42 +0200 |
| |
On Tuesday 04 July 2006 11:05, Mikael Pettersson wrote: > 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 are all slow paths where it doesn't matter.
-Andi
- 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/
| |