On Mon, Apr 28, 2008 at 4:43 PM, Christoph Hellwig <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> > > --- > > > > 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 _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
