# 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-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-gcc --version
# < git log --format=%s --max-count=1 a6fcdbf95d7907bc5d5a669adb86e6bda72d738b
# < make -s -j 10 ARCH=powerpc O=/kisskb/build/powerpc-next_85xx_stx_gp3_defconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  85xx/stx_gp3_defconfig
# make -s -j 10 ARCH=powerpc O=/kisskb/build/powerpc-next_85xx_stx_gp3_defconfig_powerpc CROSS_COMPILE=/opt/cross/kisskb/gcc-4.6.3-nolibc/powerpc-linux/bin/powerpc-linux-  
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
/kisskb/src/kernel/printk/printk.c: In function 'devkmsg_sysctl_set_loglvl':
/kisskb/src/kernel/printk/printk.c:183:16: warning: 'old' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/net/Makefile:24: CC cannot link executables. Skipping bpfilter.
/kisskb/src/drivers/dma-buf/reservation.c: In function 'reservation_object_add_shared_fence':
/kisskb/src/drivers/dma-buf/reservation.c:225:6: warning: 'k' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c: In function 'proc_reg_open':
/kisskb/src/include/linux/list.h:65:12: warning: 'pdeo' may be used uninitialized in this function [-Wuninitialized]
/kisskb/src/fs/proc/inode.c:339:21: note: 'pdeo' was declared here
/kisskb/src/fs/udf/unicode.c: In function 'udf_name_conv_char':
/kisskb/src/fs/udf/unicode.c:132:8: warning: 'c' may be used uninitialized in this function [-Wuninitialized]
INFO: Uncompressed kernel (size 0x4e8898) overlaps the address of the wrapper(0x400000)
INFO: Fixing the link_address of wrapper to (0x500000)
Image Name:   Linux-4.18.0-rc3-ga6fcdbf
Created:      Fri Aug  3 18:18:23 2018
Image Type:   PowerPC Linux Kernel Image (gzip compressed)
Data Size:    2524464 Bytes = 2465.30 kB = 2.41 MB
Load Address: 00000000
Entry Point:  00000000
Completed OK
# rm -rf /kisskb/build/powerpc-next_85xx_stx_gp3_defconfig_powerpc
# Build took: 0:01:01.154388