Messages in this thread | | | Date | Sun, 7 Aug 2022 12:02:41 +0200 | From | Ingo Molnar <> | Subject | Re: [RFC PATCH 5/5] x86/entry: Store CPU info on exception entry |
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* Borislav Petkov <bp@alien8.de> wrote:
> On Sat, Aug 06, 2022 at 11:01:06AM +0200, Ingo Molnar wrote: > > It's still 2 instructions more than what we had before, while the > > fault-time CPU number is only needed infrequently AFAICS. > > With the amount of logical cores ever increasing and how CPU packages > (nodes, L3 sharing, you name it) get more and more complex topology, > I'd say the 2 insns to show the CPU number in every exception is a good > thing to do.
We can show it - I'm arguing against extracting it too early, which costs us 2 instructions in the exception fast path - while in 99.999999999% of the cases we don't use that field at all ...
> Arguably, we probably should've even done it already...
Yeah, so I'm not against Rik's patch that prints the CPU number - that's indeed useful and I'd like to see it merged.
I'm arguing against extracting the CPU so early as to impact the exception fast path.
Thanks,
Ingo
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