linux-kernel - Re: [v2 PATCH] RISC-V: Optimize tlb flush path.

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Date:   Tue, 20 Aug 2019 20:28:36 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "hch@...radead.org" <hch@...radead.org>
CC:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "schwab@...ux-m68k.org" <schwab@...ux-m68k.org>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "allison@...utok.net" <allison@...utok.net>,
        "anup@...infault.org" <anup@...infault.org>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [v2 PATCH] RISC-V: Optimize tlb flush path.

On Tue, 2019-08-20 at 02:22 -0700, hch@...radead.org wrote:
> On Tue, Aug 20, 2019 at 08:42:19AM +0000, Atish Patra wrote:
> > cmask NULL is pretty common case and we would  be unnecessarily
> > executing bunch of instructions everytime while not saving much.
> > Kernel
> > still have to make an SBI call and OpenSBI is doing a local flush
> > anyways.
> > 
> > Looking at the code again, I think we can just use cpumask_weight
> > and
> > do local tlb flush only if local cpu is the only cpu present. 
> > 
> > Otherwise, it will just fall through and call
> > sbi_remote_sfence_vma().
> 
> Maybe it is just time to split the different cases at a higher level.
> The idea to multiple everything onto a single function always seemed
> odd to me.
> 
> FYI, here is what I do for the IPI based tlbflush for the native S-
> mode
> clint prototype, which seems much easier to understand:
> 
> http://git.infradead.org/users/hch/riscv.git/commitdiff/ea4067ae61e20fcfcf46a6f6bd1cc25710ce3afe

This does seem a lot cleaner to me. We can reuse some of the code for
this patch as well. Based on NATIVE_CLINT configuration, it will send
an IPI or SBI call.

I can rebase my patch on top of yours and I can send it together or you
can include in your series.

Let me know your preference.

-- 
Regards,
Atish