linux-kernel - Re: [External] Re: [RFC PATCH v1 0/4] riscv: mm: Defer tlb flush to context

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Message-ID: <CAPYmKFuopwQcDeCymuavTgC8crGg7Jb5Bs=hbnTtFvM+9X8HKg@mail.gmail.com>
Date: Fri, 7 Nov 2025 11:03:07 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: Guo Ren <guoren@...nel.org>
Cc: pjw@...nel.org, palmer@...belt.com, aou@...s.berkeley.edu, alex@...ti.fr, 
	apatel@...tanamicro.com, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [RFC PATCH v1 0/4] riscv: mm: Defer tlb flush to context_switch

On Fri, Nov 7, 2025 at 9:56 AM Guo Ren <guoren@...nel.org> wrote:
>
> On Thu, Oct 30, 2025 at 9:57 PM Xu Lu <luxu.kernel@...edance.com> wrote:
> >
> > When need to flush tlb of a remote cpu, there is no need to send an IPI
> > if the target cpu is not using the asid we want to flush. Instead, we
> > can cache the tlb flush info in percpu buffer, and defer the tlb flush
> > to the next context_switch.
> >
> > This reduces the number of IPI due to tlb flush:
> >
> > * ltp - mmapstress01
> > Before: ~108k
> > After: ~46k
>
> Could you add the results for these two test cases to the next version?
>
> * lmbench - lat_pagefault
> * lmbench - lat_mmap

Roger that. Thanks for your supplement.

>
> Thank you!
>
> >
> > Future plan in the next version:
> >
> > - This patch series reduces IPI by deferring tlb flush to
> > context_switch. It does not clear the mm_cpumask of target mm_struct. In
> > the next version, I will apply a threshold to the number of ASIDs
> > maintained by each cpu's tlb. Once the threshold is exceeded, ASID that
> > has not been used for the longest time will be flushed out. And current
> > cpu will be cleared in the mm_cpumask.
> >
> > Thanks in advance for your comments.
> >
> > Xu Lu (4):
> >   riscv: mm: Introduce percpu loaded_asid
> >   riscv: mm: Introduce percpu tlb flush queue
> >   riscv: mm: Enqueue tlbflush info if task is not running on target cpu
> >   riscv: mm: Perform tlb flush during context_switch
> >
> >  arch/riscv/include/asm/mmu_context.h |  1 +
> >  arch/riscv/include/asm/tlbflush.h    |  4 ++
> >  arch/riscv/mm/context.c              | 10 ++++
> >  arch/riscv/mm/tlbflush.c             | 76 +++++++++++++++++++++++++++-
> >  4 files changed, 90 insertions(+), 1 deletion(-)
> >
> > --
> > 2.20.1
> >
>
>
> --
> Best Regards
>  Guo Ren