linux-kernel - Re: [External] Re: [PATCH] RISC-V: add uniprocessor flush_tlb

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Date: Mon, 29 Jan 2024 17:38:52 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: yunhui cui <cuiyunhui@...edance.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu,
	alexghiti@...osinc.com, samuel.holland@...ive.com,
	ajones@...tanamicro.com, mchitale@...tanamicro.com,
	dylan@...estech.com, sergey.matyukevich@...tacore.com,
	prabhakar.mahadev-lad.rj@...renesas.com, apatel@...tanamicro.com,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] RISC-V: add uniprocessor
 flush_tlb_range() support

On Mon, Jan 29, 2024 at 04:26:57PM +0800, yunhui cui wrote:
> Hi Jisheng,
> 
> On Mon, Jan 29, 2024 at 4:02 PM Jisheng Zhang <jszhang@...nel.org> wrote:
> >
> > On Thu, Jan 25, 2024 at 02:20:44PM +0800, Yunhui Cui wrote:
> > > Add support for flush_tlb_range() to improve TLB performance for
> > > UP systems. In order to avoid the mutual inclusion of tlbflush.h
> > > and hugetlb.h, the UP part is also implemented in tlbflush.c.
> >
> > Hi Yunhui,
> >
> > IIRC, Samuel sent similar patch series a few weeks ago.
> >
> > https://lore.kernel.org/linux-riscv/20240102220134.3229156-1-samuel.holland@sifive.com/
> >
> > After that series, do you still need this patch?
> 
> Thank you for your reminder. I didn't find it before I mailed my
> patch. I just looked at the content of this patch. I understand that
> my patch is needed. For a single core, a more concise TLB flush logic
> is needed, and it is helpful to improve performance.

Currently, riscv UP flush_tlb_range still use flush all TLB entries,
obviously it's is a big hammer, this is what your patch is trying to
optimize. I'm not sure whether I understand your code correctly or not.
Let me know if I misunderstand your code.

After patch5 of the Samuel's series, __flush_tlb_range is unified for
SMP and UP, so that UP can also benefit from recent improvements, such
as range flush rather than all.

Thanks

> 
> Thanks,
> Yunhui