Messages in this thread | | | Date | Wed, 10 Mar 2021 15:30:03 +0100 | From | Peter Zijlstra <> | Subject | Re: The killing of ideal_nops[] |
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On Wed, Mar 10, 2021 at 03:24:47PM +0100, Peter Zijlstra wrote: > On Wed, Mar 10, 2021 at 09:13:24AM -0500, Steven Rostedt wrote: > > On Wed, 10 Mar 2021 11:22:48 +0100 > > Peter Zijlstra <peterz@infradead.org> wrote: > > > > > After this FEATURE_NOPL is unused except for required-features for > > > x86_64. FEATURE_K8 is only used for PTI and FEATURE_K7 is unused. > > > > > > AFAICT this negatively affects lots of 32bit (DONTCARE) and 32bit on > > > 64bit CPUs (CARELESS) and early AMD (K8) which is from 2003 and almost > > > 2 decades old by now (SHRUG). > > > > > > Everything x86_64 since AMD K10 (2007) was using p6_nops. > > > > > > And per FEATURE_NOPL being required for x86_64, all those CPUs can use > > > p6_nops. So stop caring about NOPs, simplify things and get on with life > > > :-) > > > > Before ripping out all the ideal_nop logic, I wonder if we should just > > force the nops you want now (that is, don't change the selected > > ideal_nops, just "pretend" that the CPU wants p6_nops), and see if anyone > > complains. After a few releases, if there's no complaints, then we can > > rip out the ideal_nop logic. > > Nah, just rip the entire thing out. You should be happy about > deterministic NOPs :-) > > NOP encoding is not something CPUs should differentiate on, that's just > bollocks.
Also, you seem to have fallen off of IRC. Anyway, weren't you the one that was complaining x86 was 'special' for having different NOPs the other day?
Fixed it ;-)
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