linux-kernel - [RFC PATCH v3 00/12] powerpc: switch VDSO to C implementation.

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Date:   Mon, 13 Jan 2020 17:08:38 +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 v3 00/12] powerpc: switch VDSO to C implementation.

This is a third tentative to switch powerpc VDSO to generic C implementation.

This version should work on PPC64 (untested). VDSO32 for PPC64 is
impossible to build and has been de-activated, because the powerpc
ASM header files for C are not prepared to build 32 bits code with CONFIG_PPC64.

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 need to be performed in ASM.

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

The first patch adds VDSO generic C support without any changes to common code.
Performance is as follows:

gettimeofday:    vdso: 1379 nsec/call
clock-getres-realtime-coarse:    vdso: 984 nsec/call
clock-gettime-realtime-coarse:    vdso: 868 nsec/call
clock-getres-realtime:    vdso: 922 nsec/call
clock-gettime-realtime:    vdso: 1511 nsec/call
clock-getres-monotonic-raw:    vdso: 968 nsec/call
clock-gettime-monotonic-raw:    vdso: 1576 nsec/call

Then a few changes in the common code have allowed performance improvement. At
the end of the series we have:

gettimeofday:    vdso: 899 nsec/call
clock-getres-realtime-coarse:    vdso: 546 nsec/call
clock-gettime-realtime-coarse:    vdso: 615 nsec/call
clock-getres-realtime:    vdso: 545 nsec/call
clock-gettime-realtime:    vdso: 1064 nsec/call
clock-getres-monotonic-raw:    vdso: 546 nsec/call
clock-gettime-monotonic-raw:    vdso: 1125 nsec/call

Christophe Leroy (12):
  powerpc/64: Don't provide time functions in compat VDSO32
  powerpc/vdso: Switch VDSO to generic C implementation.
  lib: vdso: mark __cvdso_clock_getres() as static
  lib: vdso: inline do_hres() and do_coarse()
  lib: vdso: Avoid duplication in __cvdso_clock_getres()
  lib: vdso: __iter_div_u64_rem() is suboptimal for 32 bit time
  powerpc/vdso: simplify __get_datapage()
  lib: vdso: allow arches to provide vdso data pointer
  powerpc/vdso: provide inline alternative to __get_datapage()
  powerpc/vdso: provide vdso data pointer from the ASM caller.
  lib: vdso: split clock verification out of __arch_get_hw_counter()
  powerpc/vdso: provide __arch_is_hw_counter_valid()

 arch/powerpc/Kconfig                         |   2 +
 arch/powerpc/include/asm/vdso/gettimeofday.h | 104 +++++++++++
 arch/powerpc/include/asm/vdso/vsyscall.h     |  25 +++
 arch/powerpc/include/asm/vdso_datapage.h     |  52 +++---
 arch/powerpc/kernel/asm-offsets.c            |  46 +----
 arch/powerpc/kernel/time.c                   |  90 ----------
 arch/powerpc/kernel/vdso.c                   |  58 ++----
 arch/powerpc/kernel/vdso32/Makefile          |  30 +++-
 arch/powerpc/kernel/vdso32/datapage.S        |  10 +-
 arch/powerpc/kernel/vdso32/gettimeofday.S    | 258 ++++-----------------------
 arch/powerpc/kernel/vdso32/vdso32.lds.S      |   9 +-
 arch/powerpc/kernel/vdso32/vgettimeofday.c   |  29 +++
 arch/powerpc/kernel/vdso64/Makefile          |  23 ++-
 arch/powerpc/kernel/vdso64/datapage.S        |  13 +-
 arch/powerpc/kernel/vdso64/gettimeofday.S    | 257 ++++----------------------
 arch/powerpc/kernel/vdso64/vdso64.lds.S      |   7 +-
 arch/powerpc/kernel/vdso64/vgettimeofday.c   |  29 +++
 lib/vdso/gettimeofday.c                      | 130 +++++++++++---
 18 files changed, 457 insertions(+), 715 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
 create mode 100644 arch/powerpc/kernel/vdso64/vgettimeofday.c

-- 
2.13.3