linux-kernel - Re: [PATCH v2 2/2] mm/mmu_gather: send tlb_remove_table_smp

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Message-ID: <cccb5351e48b11e6c657bcfa28632f49cb9cc800.camel@redhat.com>
Date:   Mon, 26 Jun 2023 17:36:28 +0300
From:   ypodemsk@...hat.com
To:     Dave Hansen <dave.hansen@...el.com>, mtosatti@...hat.com,
        ppandit@...hat.com, david@...hat.com, linux@...linux.org.uk,
        mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        hca@...ux.ibm.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, svens@...ux.ibm.com,
        davem@...emloft.net, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        keescook@...omium.org, paulmck@...nel.org, frederic@...nel.org,
        will@...nel.org, peterz@...radead.org, ardb@...nel.org,
        samitolvanen@...gle.com, juerg.haefliger@...onical.com,
        arnd@...db.de, rmk+kernel@...linux.org.uk, geert+renesas@...der.be,
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        aneesh.kumar@...ux.ibm.com, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] mm/mmu_gather: send tlb_remove_table_smp_sync
 IPI only to MM CPUs

On Thu, 2023-06-22 at 06:37 -0700, Dave Hansen wrote:
> On 6/22/23 06:14, ypodemsk@...hat.com wrote:
> > I will send a new version with the local variable as you suggested
> > soon.
> > As for the config name, what about CONFIG_ARCH_HAS_MM_CPUMASK?
> 
> The confusing part about that name is that mm_cpumask() and
> mm->cpu_bitmap[] are defined unconditionally.  So, they're *around*
> unconditionally but just aren't updated.
> 
I think your right about the config name,
How about the
CONFIG_ARCH_USE_MM_CPUMASK?
This has the right semantic as these archs use the cpumask field of the
mm struct.

> BTW, it would also be nice to have _some_ kind of data behind this
> patch.
> 
> Fewer IPIs are better I guess, but it would still be nice if you
> could say:
> 
> 	Before this patch, /proc/interrupts showed 123 IPIs/hour for an
> 	isolated CPU.  After the approach here, it was 0.
> 
> ... or something.

This is part of an ongoing effort to remove IPIs and this one was found
via code inspection.