# git rev-parse -q --verify a6fcdbf95d7907bc5d5a669adb86e6bda72d738b^{commit}
a6fcdbf95d7907bc5d5a669adb86e6bda72d738b
already have revision, skipping fetch
# git checkout -q -f -B kisskb a6fcdbf95d7907bc5d5a669adb86e6bda72d738b
# git clean -qxdf
# < git log -1
# commit a6fcdbf95d7907bc5d5a669adb86e6bda72d738b
# Author: Reza Arbab <arbab@linux.ibm.com>
# Date:   Thu Aug 2 23:03:36 2018 -0500
# 
#     powerpc/powernv: Fix concurrency issue with npu->mmio_atsd_usage
#     
#     We've encountered a performance issue when multiple processors stress
#     {get,put}_mmio_atsd_reg(). These functions contend for
#     mmio_atsd_usage, an unsigned long used as a bitmask.
#     
#     The accesses to mmio_atsd_usage are done using test_and_set_bit_lock()
#     and clear_bit_unlock(). As implemented, both of these will require
#     a (successful) stwcx to that same cache line.
#     
#     What we end up with is thread A, attempting to unlock, being slowed by
#     other threads repeatedly attempting to lock. A's stwcx instructions
#     fail and retry because the memory reservation is lost every time a
#     different thread beats it to the punch.
#     
#     There may be a long-term way to fix this at a larger scale, but for
#     now resolve the immediate problem by gating our call to
#     test_and_set_bit_lock() with one to test_bit(), which is obviously
#     implemented without using a store.
#     
#     Fixes: 1ab66d1fbada ("powerpc/powernv: Introduce address translation services for Nvlink2")
#     Signed-off-by: Reza Arbab <arbab@linux.ibm.com>
#     Acked-by: Alistair Popple <alistair@popple.id.au>
#     Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
# < /opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-gcc --version
# < git log --format=%s --max-count=1 a6fcdbf95d7907bc5d5a669adb86e6bda72d738b
# < make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_powerpc-allmodconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  allmodconfig
# Added to kconfig CONFIG_BUILD_DOCSRC=n
# Added to kconfig CONFIG_MODULE_SIG=n
# Added to kconfig CONFIG_SAMPLES=n
# yes \n | make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_powerpc-allmodconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  oldconfig
yes: standard output: Broken pipe
yes: write error
# make -s -j 48 ARCH=powerpc O=/kisskb/build/powerpc-next_powerpc-allmodconfig_powerpc-5.3 CROSS_COMPILE=/opt/cross/kisskb/gcc-5.3.0-nolibc/powerpc64-linux/bin/powerpc64-linux-  
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
/kisskb/src/sound/aoa/codecs/onyx.c: In function 'onyx_snd_single_bit_get':
/kisskb/src/sound/aoa/codecs/onyx.c:380:37: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
  ucontrol->value.integer.value[0] = !!(c & mask) ^ polarity;
                                     ^
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
In file included from /kisskb/src/include/linux/io.h:25:0,
                 from /kisskb/src/include/linux/of_address.h:7,
                 from /kisskb/src/drivers/ata/ahci_qoriq.c:18:
/kisskb/src/drivers/ata/ahci_qoriq.c: In function 'ahci_qoriq_hardreset':
/kisskb/src/arch/powerpc/include/asm/io.h:633:3: warning: 'px_is' may be used uninitialized in this function [-Wmaybe-uninitialized]
   ppc_pci_io.name al;    \
   ^
/kisskb/src/drivers/ata/ahci_qoriq.c:86:14: note: 'px_is' was declared here
  u32 px_cmd, px_is, px_val;
              ^
In file included from /kisskb/src/include/linux/io.h:25:0,
                 from /kisskb/src/include/linux/of_address.h:7,
                 from /kisskb/src/drivers/ata/ahci_qoriq.c:18:
/kisskb/src/arch/powerpc/include/asm/io.h:142:2: warning: 'px_cmd' may be used uninitialized in this function [-Wmaybe-uninitialized]
  __asm__ __volatile__("sync;"#insn" %1,%y0"   \
  ^
/kisskb/src/drivers/ata/ahci_qoriq.c:86:6: note: 'px_cmd' was declared here
  u32 px_cmd, px_is, px_val;
      ^
Completed OK
# rm -rf /kisskb/build/powerpc-next_powerpc-allmodconfig_powerpc-5.3
# Build took: 0:18:15.657713