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Date:   Tue, 20 Aug 2019 02:22:07 -0700
From:   "hch@infradead.org" <hch@infradead.org>
To:     Atish Patra <Atish.Patra@wdc.com>
Cc:     "schwab@linux-m68k.org" <schwab@linux-m68k.org>,
        "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
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        "allison@lohutok.net" <allison@lohutok.net>,
        "anup@brainfault.org" <anup@brainfault.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "hch@infradead.org" <hch@infradead.org>,
        "palmer@sifive.com" <palmer@sifive.com>
Subject: Re: [v2 PATCH] RISC-V: Optimize tlb flush path.
Message-ID: <20190820092207.GA26271@infradead.org>
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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