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From: Vipin Sharma <vipinsh@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Matlack <dmatlack@google.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm list <kvm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] KVM: x86/mmu: Speed up slot_rmap_walk_next for sparsely populated rmaps
Date: Fri, 8 Apr 2022 12:31:21 -0700	[thread overview]
Message-ID: <CAHVum0d=WoqxZ4vUYY37jeQL1yLdiwbYjPSPFAa1meM5LUBDQQ@mail.gmail.com> (raw)
In-Reply-To: <b754fa0a-4f9e-1ea5-6c77-f2410b7f8456@redhat.com>

On Sun, Mar 27, 2022 at 3:41 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 3/26/22 01:31, Vipin Sharma wrote:
> >>> -static void slot_rmap_walk_next(struct slot_rmap_walk_iterator *iterator)
> >>> +static noinline void
> >>
> >> What is the reason to add noinline?
> >
> > My understanding is that since this method is called from
> > __always_inline methods, noinline will avoid gcc inlining the
> > slot_rmap_walk_next in those functions and generate smaller code.
> >
>
> Iterators are written in such a way that it's way more beneficial to
> inline them.  After inlining, compilers replace the aggregates (in this
> case, struct slot_rmap_walk_iterator) with one variable per field and
> that in turn enables a lot of optimizations, so the iterators should
> actually be always_inline if anything.
>
> For the same reason I'd guess the effect on the generated code should be
> small (next time please include the output of "size mmu.o"), but should
> still be there.  I'll do a quick check of the generated code and apply
> the patch.
>
> Paolo
>

Let me know if you are still planning to modify the current patch by
removing "noinline" and merge or if you prefer a v2 without noinline.

Thanks
Vipin

  parent reply	other threads:[~2022-04-08 19:32 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-25 23:31 [PATCH] KVM: x86/mmu: Speed up slot_rmap_walk_next for sparsely populated rmaps Vipin Sharma
2022-03-25 23:52 ` David Matlack
2022-03-26  0:31   ` Vipin Sharma
2022-03-27 10:40     ` Paolo Bonzini
2022-03-28 19:13       ` Vipin Sharma
2022-03-28 20:29         ` Sean Christopherson
2022-04-08 19:31       ` Vipin Sharma [this message]
2022-04-18 16:29         ` Vipin Sharma
2022-04-26 20:33           ` Vipin Sharma

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