linux-kernel - Re: [PATCH 04/10] x86,mm: use INVLPGB for kernel TLB flushes

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Message-ID: <86a2ca80d2be3a943566473ea156180abf3b2557.camel@surriel.com>
Date: Sun, 22 Dec 2024 10:12:56 -0500
From: Rik van Riel <riel@...riel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, kernel-team@...a.com, 
	dave.hansen@...ux.intel.com, luto@...nel.org, tglx@...utronix.de,
 mingo@...hat.com, 	bp@...en8.de, hpa@...or.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 04/10] x86,mm: use INVLPGB for kernel TLB flushes

On Sun, 2024-12-22 at 12:16 +0100, Peter Zijlstra wrote:
> On Sat, Dec 21, 2024 at 11:06:36PM -0500, Rik van Riel wrote:
> > Use broadcast TLB invalidation for kernel addresses when available.
> > 
> > +static void broadcast_kernel_range_flush(unsigned long start,
> > unsigned long end)
> > +{
> > +	unsigned long addr;
> > +	unsigned long maxnr = boot_cpu_data.invlpgb_count_max;
> > +	unsigned long threshold = tlb_single_page_flush_ceiling *
> > maxnr;
> > +
> > +	/*
> > +	 * TLBSYNC only waits for flushes originating on the same
> > CPU.
> > +	 * Disabling migration allows us to wait on all flushes.
> > +	 */
> > +	migrate_disable();
> 
> So how expensive is all this? That is, I think I would feel better is
> this were preempt_disable().

Either should work. If preempt_disable() is cheaper,
I'm happy to use that.

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