linux-kernel - Re: [PATCH V3 4/7] x86/entry: move PUSH_AND_CLEAR_REGS out of error

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Date:   Thu, 17 Mar 2022 00:18:12 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH V3 4/7] x86/entry: move PUSH_AND_CLEAR_REGS out of error_entry

On Wed, Mar 16, 2022 at 11:07 PM Peter Zijlstra <peterz@...radead.org> wrote:

>
> So I don't much care about the orc data, that's only used when
> unwinding, a relatively rare occasion, anyway. But the text increase
> does bother me a little, this can blow up I$ misses on syscall heavy
> workloads.

It has nothing to do with the syscall.

It does add a lot in I$.  But it is fortunate that the footprint
is the same (before and after the patch) for a single exception vector.
For example heavy #PF workloads.

Footprint will increase after this patch when two or more exception
vectors happen heavily at the same time, for example when #PF and
timer are occurring heavily.

We can put PUSH_AND_CLEAR_REGS in a single function to reduce the
footprint for heavy multi-exception workloads.  What do you think?