From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@intel.com>,
ira.weiny@intel.com, Rik van Riel <riel@surriel.com>,
x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [RFC PATCH 5/5] x86/entry: Store CPU info on exception entry
Date: Sun, 7 Aug 2022 12:02:41 +0200 [thread overview]
Message-ID: <Yu+Nwbn4CZUmyD14@gmail.com> (raw)
In-Reply-To: <Yu4wON0MRGH7h5Jv@zn.tnic>
* 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
next prev parent reply other threads:[~2022-08-07 10:03 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-05 17:30 [RFC PATCH 0/5] Print CPU at segfault time ira.weiny
2022-08-05 17:30 ` [RFC PATCH 1/5] entry: Pass pt_regs to irqentry_exit_cond_resched() ira.weiny
2022-08-05 18:33 ` Rik van Riel
2022-08-08 10:38 ` Borislav Petkov
2022-08-08 17:34 ` Ira Weiny
2022-08-08 17:38 ` Borislav Petkov
2022-08-08 17:43 ` Dave Hansen
2022-08-08 17:52 ` Borislav Petkov
2022-08-09 23:18 ` Thomas Gleixner
2022-08-10 7:25 ` Thomas Gleixner
2022-08-05 17:30 ` [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs ira.weiny
2022-08-05 18:34 ` Rik van Riel
2022-08-09 12:05 ` Borislav Petkov
2022-08-09 18:38 ` Ira Weiny
2022-08-09 18:49 ` Borislav Petkov
2022-08-09 21:14 ` Thomas Gleixner
2022-08-09 21:38 ` Borislav Petkov
2022-08-09 22:33 ` Ira Weiny
2022-08-09 21:49 ` Ira Weiny
2022-08-09 23:53 ` Thomas Gleixner
2022-08-05 17:30 ` [RFC PATCH 3/5] x86/entry: Add auxiliary pt_regs space ira.weiny
2022-08-05 18:45 ` Rik van Riel
2022-08-05 17:30 ` [RFC PATCH 4/5] x86,mm: print likely CPU at segfault time ira.weiny
2022-08-05 17:30 ` [RFC PATCH 5/5] x86/entry: Store CPU info on exception entry ira.weiny
2022-08-05 18:46 ` Rik van Riel
2022-08-05 18:47 ` Dave Hansen
2022-08-06 9:01 ` Ingo Molnar
2022-08-06 9:11 ` Borislav Petkov
2022-08-07 10:02 ` Ingo Molnar [this message]
2022-08-07 10:35 ` Borislav Petkov
2022-08-07 20:02 ` Ira Weiny
2022-08-08 11:03 ` Ingo Molnar
2022-08-08 12:01 ` Borislav Petkov
2022-08-09 20:06 ` Thomas Gleixner
2022-08-08 16:16 ` Dave Hansen
2022-08-08 17:24 ` Rik van Riel
2022-08-09 21:19 ` Andy Lutomirski
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