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From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Hansen <dave.hansen@intel.com>, LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Andrew Cooper <andrew.cooper3@citrix.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Subject: Re: [patch 3/3] x86/fpu/xsave: Optimize XSAVEC/S when XGETBV1 is supported
Date: Tue, 19 Apr 2022 15:43:01 +0200	[thread overview]
Message-ID: <87ee1t9oka.ffs@tglx> (raw)
In-Reply-To: <a93e6d3f-e8b9-2fab-1139-a8ba3dc4820b@intel.com>

On Thu, Apr 14 2022 at 10:24, Dave Hansen wrote:
> On 4/4/22 05:11, Thomas Gleixner wrote:
>> which is suboptimal. Prefetch works better when the access is linear. But
>> what's worse is that PKRU can be located in a different page which
>> obviously affects dTLB.
>
> The numbers don't lie, but I'm still surprised by this.  Was this in a
> VM that isn't backed with large pages?  task_struct.thread.fpu is
> kmem_cache_alloc()'d and is in the direct map, which should be 2M/1G
> pages almost all the time.

Hmm. Indeed, that's weird.

That was bare metal and I just checked that this was a production config
and not some weird debug muck which breaks large pages. I'll look deeper
into that.

Thanks,

        tglx




  reply	other threads:[~2022-04-19 13:48 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-04 12:11 [patch 0/3] x86/fpu/xsave: Add XSAVEC support and XGETBV1 utilization Thomas Gleixner
2022-04-04 12:11 ` [patch 1/3] x86/fpu/xsave: Support XSAVEC in the kernel Thomas Gleixner
2022-04-04 16:10   ` Andrew Cooper
2022-04-14 14:43   ` Dave Hansen
2022-04-25 13:11   ` [tip: x86/fpu] " tip-bot2 for Thomas Gleixner
2022-04-04 12:11 ` [patch 2/3] x86/fpu/xsave: Prepare for optimized compaction Thomas Gleixner
2022-04-14 15:46   ` Dave Hansen
2022-04-19 12:39     ` Thomas Gleixner
2022-04-19 13:33       ` Thomas Gleixner
2022-04-04 12:11 ` [patch 3/3] x86/fpu/xsave: Optimize XSAVEC/S when XGETBV1 is supported Thomas Gleixner
2022-04-14 17:24   ` Dave Hansen
2022-04-19 13:43     ` Thomas Gleixner [this message]
2022-04-19 21:22       ` Thomas Gleixner
2022-04-20 18:15         ` Tom Lendacky
2022-04-22 19:30           ` Thomas Gleixner
2022-04-23 15:20             ` Dave Hansen

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