[External] Re: [PATCH] RISC-V: add uniprocessor flush_tlb_range() support

[yunhui cui]

Hi Jisheng,

On Mon, Jan 29, 2024 at 5:51 PM Jisheng Zhang <jszhang at kernel.org> wrote:
>
> 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 at kernel.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.

In my opinion, UP does not need to combine some SMP if... else,
on_each_cpu(...) logic, which is also a manifestation of performance
improvement. what do you think?
Thanks,
Yunhui