linux-kernel - Re: [PATCH v3 3/3] RISC-V: Do not invoke SBI call if cpumask is empty

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Message-ID: <bfec8818b825fd791f7e170ba913860971c18067.camel@wdc.com>
Date:   Thu, 22 Aug 2019 04:23:23 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "hch@....de" <hch@....de>
CC:     "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "schwab@...ux-m68k.org" <schwab@...ux-m68k.org>,
        Anup Patel <Anup.Patel@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>
Subject: Re: [PATCH v3 3/3] RISC-V: Do not invoke SBI call if cpumask is empty

On Thu, 2019-08-22 at 03:51 +0200, Christoph Hellwig wrote:
> On Wed, Aug 21, 2019 at 05:46:44PM -0700, Atish Patra wrote:
> > SBI calls are expensive. If cpumask is empty, there is no need to
> > trap via SBI as no remote tlb flushing is required.
> > 
> > Signed-off-by: Atish Patra <atish.patra@....com>
> > ---
> >  arch/riscv/mm/tlbflush.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> > index 9f58b3790baa..2bd3c418d769 100644
> > --- a/arch/riscv/mm/tlbflush.c
> > +++ b/arch/riscv/mm/tlbflush.c
> > @@ -21,6 +21,9 @@ static void __sbi_tlb_flush_range(struct cpumask
> > *cmask, unsigned long start,
> >  		goto issue_sfence;
> >  	}
> >  
> > +	if (cpumask_empty(cmask))
> > +		goto done;
> 
> I think this can even be done before the get_cpu to optimize it a
> little
> further.

Yeah. I can just return directly in this case and call get_cpu after
this. Thanks for the suggestion.


-- 
Regards,
Atish