linux-kernel - [RFC PATCH v2 00/10] powerpc/32: switch VDSO to C implementation.

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Date:   Mon, 23 Dec 2019 14:31:01 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>, arnd@...db.de,
        tglx@...utronix.de, vincenzo.frascino@....com, luto@...nel.org
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        x86@...nel.org
Subject: [RFC PATCH v2 00/10] powerpc/32: switch VDSO to C implementation.

This is a second tentative to switch powerpc/32 vdso to generic C implementation.

It will likely not work on 64 bits or even build properly at the moment.

powerpc is a bit special for VDSO as well as system calls in the
way that it requires setting CR SO bit which cannot be done in C.
Therefore, entry/exit and fallback needs to be performed in ASM.

To allow that, the fallback calls are moved out of the common code
and left to the arches.

A few other changes in the common code have allowed performance improvement.

The performance has improved since first RFC, but it is still lower than
current assembly VDSO.

On a powerpc8xx, with current powerpc/32 ASM VDSO:

gettimeofday:    vdso: 737 nsec/call
clock-getres-realtime:    vdso: 475 nsec/call
clock-gettime-realtime:    vdso: 892 nsec/call
clock-getres-monotonic:    vdso: 475 nsec/call
clock-gettime-monotonic:    vdso: 1014 nsec/call

First try of C implementation:

gettimeofday:    vdso: 1533 nsec/call
clock-getres-realtime:    vdso: 853 nsec/call
clock-gettime-realtime:    vdso: 1570 nsec/call
clock-getres-monotonic:    vdso: 835 nsec/call
clock-gettime-monotonic:    vdso: 1605 nsec/call

With this series:

gettimeofday:    vdso: 1016 nsec/call
clock-getres-realtime:    vdso: 560 nsec/call
clock-gettime-realtime:    vdso: 1192 nsec/call
clock-getres-monotonic:    vdso: 560 nsec/call
clock-gettime-monotonic:    vdso: 1192 nsec/call


Changes made to other arches are untested, not even compiled.


Christophe Leroy (10):
  lib: vdso: ensure all arches have 32bit fallback
  lib: vdso: move call to fallback out of common code.
  lib: vdso: Change __cvdso_clock_gettime/getres_common() to
    __cvdso_clock_gettime/getres()
  lib: vdso: get pointer to vdso data from the arch
  lib: vdso: inline do_hres()
  lib: vdso: make do_coarse() return 0
  lib: vdso: don't use READ_ONCE() in __c_kernel_time()
  lib: vdso: Avoid duplication in __cvdso_clock_getres()
  powerpc/vdso32: inline __get_datapage()
  powerpc/32: Switch VDSO to C implementation.

 arch/arm/include/asm/vdso/gettimeofday.h          |  26 +++
 arch/arm/vdso/vgettimeofday.c                     |  32 ++-
 arch/arm64/include/asm/vdso/compat_gettimeofday.h |   2 -
 arch/arm64/include/asm/vdso/gettimeofday.h        |  26 +++
 arch/arm64/kernel/vdso/vgettimeofday.c            |  24 +-
 arch/arm64/kernel/vdso32/vgettimeofday.c          |  39 +++-
 arch/mips/include/asm/vdso/gettimeofday.h         |  28 ++-
 arch/mips/vdso/vgettimeofday.c                    |  56 ++++-
 arch/powerpc/Kconfig                              |   2 +
 arch/powerpc/include/asm/vdso/gettimeofday.h      |  45 ++++
 arch/powerpc/include/asm/vdso/vsyscall.h          |  27 +++
 arch/powerpc/include/asm/vdso_datapage.h          |  28 +--
 arch/powerpc/kernel/asm-offsets.c                 |  23 +-
 arch/powerpc/kernel/time.c                        |  92 +-------
 arch/powerpc/kernel/vdso.c                        |  19 +-
 arch/powerpc/kernel/vdso32/Makefile               |  19 +-
 arch/powerpc/kernel/vdso32/cacheflush.S           |   9 +-
 arch/powerpc/kernel/vdso32/datapage.S             |  28 +--
 arch/powerpc/kernel/vdso32/gettimeofday.S         | 265 +++-------------------
 arch/powerpc/kernel/vdso32/vgettimeofday.c        |  32 +++
 arch/x86/entry/vdso/vclock_gettime.c              |  52 ++++-
 arch/x86/include/asm/vdso/gettimeofday.h          |  28 ++-
 lib/vdso/gettimeofday.c                           | 100 +++-----
 23 files changed, 505 insertions(+), 497 deletions(-)
 create mode 100644 arch/powerpc/include/asm/vdso/gettimeofday.h
 create mode 100644 arch/powerpc/include/asm/vdso/vsyscall.h
 create mode 100644 arch/powerpc/kernel/vdso32/vgettimeofday.c

-- 
2.13.3