Messages in this thread | | | From | Con Kolivas <> | Subject | Re: [PATCH] 2.6.1 Hyperthread smart "nice" 2 | Date | Tue, 3 Feb 2004 22:14:49 +1100 |
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On Tue, 3 Feb 2004 22:12, Ingo Molnar wrote: > * Con Kolivas <kernel@kolivas.org> wrote: > > > for lowprio tasks they are of little use, unless you modify gcc to > > > sprinkle mwait yields all around the 'lowprio code' - not very > > > practical i think. > > > > Yuck! > > > > Looks like the kernel is the only thing likely to be smart enough to > > do this correctly for some time yet. > > no, there's no way for the kernel to do this 'correctly', without > further hardware help. mwait is suspending the current virtual CPU a bit > better than rep-nop did. This can be exploited for the idle loop because > the idle loop does nothing so it can execute the rep-nop. (mwait can > likely also be used for spinlocks but that is another issue.) > > user-space code that is 'low-prio' cannot be slowed down via mwait, > without interleaving user-space instructions with mwait (or with > rep-nop). > > this is a problem area that is not solved by mwait - giving priority to > virtual CPUs should be offered by CPUs, once the number of logical cores > increases significantly - if the interaction between those cores is > significant. (there are SMT designs where this isnt an issue.)
Actually I was trying to say something like my patch, but done correctly. I agree with new instructions not helping at the moment.
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