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Date: Fri, 9 Feb 2018 20:25:15 +0100
From: Joerg Roedel <jroedel@suse.de>
Subject: Re: [PATCH 09/31] x86/entry/32: Leave the kernel via trampoline stack
Message-ID: <20180209192515.qvvixkn5rz77oz6l@suse.de>
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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Joerg Roedel <joro@8bytes.org>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>, the arch/x86 maintainers <x86@kernel.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, linux-mm <linux-mm@kvack.org>, Andy Lutomirski <luto@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Juergen Gross <jgross@suse.com>, Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Brian Gerst <brgerst@gmail.com>, David Laight <David.Laight@aculab.com>, Denys Vlasenko <dvlasenk@redhat.com>, Eduardo Valentin <eduval@amazon.com>, Greg KH <gregkh@linuxfoundation.org>, Will Deacon <will.deacon@arm.com>, "Liguori, Anthony" <aliguori@amazon.com>, Daniel Gruss <daniel.gruss@iaik.tugraz.at>, Hugh Dickins <hughd@google.com>, Kees Cook <keescook@google.com>, Andrea Arcangeli <aarcange@redhat.com>, Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>

On Fri, Feb 09, 2018 at 11:17:35AM -0800, Linus Torvalds wrote:
> Yeah, it's only true on the very latest uarchs, and even there it's
> not perfect for small copies.
> 
> On the older machines that are relevant for 32-bit code, it's often
> tens of cycles just for the ucode overhead, I think, and "rep movsb"
> actually does things literally a byte at a time.

Ugh, okay. So I switch to movsl, that should at least perform on-par
with the chain of 'pushl' instructions I had before.


Thanks,

	Joerg

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