From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk" Subject: Re: [PATCH] Add fast little-endian switch system call Date: Mon, 28 Apr 2008 17:42:18 +0200 Message-ID: References: <18453.18943.906693.409245@cargo.ozlabs.ibm.com> <20080428144332.GA17109@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080428144332.GA17109-jcswGhMUV9g@public.gmane.org> Content-Disposition: inline Sender: linux-arch-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: To: Christoph Hellwig Cc: Paul Mackerras , linuxppc-dev-mnsaURCQ41sdnm+yROfE0A@public.gmane.org, mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-arch-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Mon, Apr 28, 2008 at 4:43 PM, Christoph Hellwig wrote: > Please see Michael Kerrisk on userspace ABI updates. A nice little > manpage for this gimmick would be helpful, and maybe help other > platforms that want one aswell to implement the same API. Thanks Chrsitoph. I'm not on any of these lists at the moment. Paul -- is this syscall defintely going in? Could you write a short description for userland programmers? I'll do the grotty *roff stuff. > On Mon, Apr 28, 2008 at 01:52:31PM +1000, Paul Mackerras wrote: > > This adds a system call on 64-bit platforms for switching between > > little-endian and big-endian modes that is much faster than doing a > > prctl call. This system call is handled as a special case right at > > the start of the system call entry code, and because it is a special > > case, it uses a system call number which is out of the range of > > normal system calls, namely 0x1ebe. > > > > Measurements with lmbench on a 4.2GHz POWER6 showed no measurable > > change in the speed of normal system calls with this patch. > > > > Switching endianness with this new system call takes around 60ns on a > > 4.2GHz POWER6, compared with around 300ns to switch endian mode with a > > prctl. This can provide a significant performance advantage for > > emulators for little-endian architectures that want to switch between > > big-endian and little-endian mode frequently, e.g. because they are > > generating instructions sequences on the fly and they want to run > > those sequences in little-endian mode. > > > > Signed-off-by: Paul Mackerras > > --- > > > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S > > index 215973a..2eb49a7 100644 > > --- a/arch/powerpc/kernel/head_64.S > > +++ b/arch/powerpc/kernel/head_64.S > > @@ -239,6 +239,10 @@ instruction_access_slb_pSeries: > > .globl system_call_pSeries > > system_call_pSeries: > > HMT_MEDIUM > > +BEGIN_FTR_SECTION > > + cmpdi r0,0x1ebe > > + beq- 1f > > +END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) > > Am I missing something here or does this add a branch for every normal > syscall? > > > mr r9,r13 > > mfmsr r10 > > mfspr r13,SPRN_SPRG3 > > @@ -253,6 +257,13 @@ system_call_pSeries: > > rfid > > b . /* prevent speculative execution */ > > > > +/* Fast LE/BE switch system call */ > > +1: mfspr r12,SPRN_SRR1 > > + xori r12,r12,MSR_LE > > + mtspr SPRN_SRR1,r12 > > + rfid /* return to userspace */ > > + b . > > + > > STD_EXCEPTION_PSERIES(0xd00, single_step) > > STD_EXCEPTION_PSERIES(0xe00, trap_0e) > > > > _______________________________________________ > > Linuxppc-dev mailing list > > Linuxppc-dev-mnsaURCQ41sdnm+yROfE0A@public.gmane.org > > https://ozlabs.org/mailman/listinfo/linuxppc-dev > ---end quoted text--- > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from qb-out-0506.google.com ([72.14.204.232]:43571 "EHLO qb-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935526AbYD1PmW (ORCPT ); Mon, 28 Apr 2008 11:42:22 -0400 Received: by qb-out-0506.google.com with SMTP id e11so2953371qbe.15 for ; Mon, 28 Apr 2008 08:42:18 -0700 (PDT) Message-ID: Date: Mon, 28 Apr 2008 17:42:18 +0200 From: "Michael Kerrisk" Subject: Re: [PATCH] Add fast little-endian switch system call In-Reply-To: <20080428144332.GA17109@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <18453.18943.906693.409245@cargo.ozlabs.ibm.com> <20080428144332.GA17109@lst.de> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Christoph Hellwig Cc: Paul Mackerras , linuxppc-dev@ozlabs.org, mtk.manpages@gmail.com, linux-arch@vger.kernel.org Message-ID: <20080428154218.oS9MERPUugn5vH1fdkjWAetKl6rdZBuvc98yE1MYFrw@z> On Mon, Apr 28, 2008 at 4:43 PM, Christoph Hellwig wrote: > Please see Michael Kerrisk on userspace ABI updates. A nice little > manpage for this gimmick would be helpful, and maybe help other > platforms that want one aswell to implement the same API. Thanks Chrsitoph. I'm not on any of these lists at the moment. Paul -- is this syscall defintely going in? Could you write a short description for userland programmers? I'll do the grotty *roff stuff. > On Mon, Apr 28, 2008 at 01:52:31PM +1000, Paul Mackerras wrote: > > This adds a system call on 64-bit platforms for switching between > > little-endian and big-endian modes that is much faster than doing a > > prctl call. This system call is handled as a special case right at > > the start of the system call entry code, and because it is a special > > case, it uses a system call number which is out of the range of > > normal system calls, namely 0x1ebe. > > > > Measurements with lmbench on a 4.2GHz POWER6 showed no measurable > > change in the speed of normal system calls with this patch. > > > > Switching endianness with this new system call takes around 60ns on a > > 4.2GHz POWER6, compared with around 300ns to switch endian mode with a > > prctl. This can provide a significant performance advantage for > > emulators for little-endian architectures that want to switch between > > big-endian and little-endian mode frequently, e.g. because they are > > generating instructions sequences on the fly and they want to run > > those sequences in little-endian mode. > > > > Signed-off-by: Paul Mackerras > > --- > > > > diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S > > index 215973a..2eb49a7 100644 > > --- a/arch/powerpc/kernel/head_64.S > > +++ b/arch/powerpc/kernel/head_64.S > > @@ -239,6 +239,10 @@ instruction_access_slb_pSeries: > > .globl system_call_pSeries > > system_call_pSeries: > > HMT_MEDIUM > > +BEGIN_FTR_SECTION > > + cmpdi r0,0x1ebe > > + beq- 1f > > +END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) > > Am I missing something here or does this add a branch for every normal > syscall? > > > mr r9,r13 > > mfmsr r10 > > mfspr r13,SPRN_SPRG3 > > @@ -253,6 +257,13 @@ system_call_pSeries: > > rfid > > b . /* prevent speculative execution */ > > > > +/* Fast LE/BE switch system call */ > > +1: mfspr r12,SPRN_SRR1 > > + xori r12,r12,MSR_LE > > + mtspr SPRN_SRR1,r12 > > + rfid /* return to userspace */ > > + b . > > + > > STD_EXCEPTION_PSERIES(0xd00, single_step) > > STD_EXCEPTION_PSERIES(0xe00, trap_0e) > > > > _______________________________________________ > > Linuxppc-dev mailing list > > Linuxppc-dev@ozlabs.org > > https://ozlabs.org/mailman/listinfo/linuxppc-dev > ---end quoted text--- > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html