Revision c4bfa3f5f906aee2e084c5b1fb15caf876338ef8 authored by Peter Zijlstra on 17 June 2015, 12:29:24 UTC, committed by Thomas Gleixner on 18 June 2015, 22:09:56 UTC
Introduce raw_write_seqcount_barrier(), a new construct that can be used to provide write barrier semantics in seqcount read loops instead of the usual consistency guarantee. raw_write_seqcount_barier() is equivalent to: raw_write_seqcount_begin(); raw_write_seqcount_end(); But avoids issueing two back-to-back smp_wmb() instructions. This construct works because the read side will 'stall' when observing odd values. This means that -- referring to the example in the comment below -- even though there is no (matching) read barrier between the loads of X and Y, we cannot observe !x && !y, because: - if we observe Y == false we must observe the first sequence increment, which makes us loop, until - we observe !(seq & 1) -- the second sequence increment -- at which time we must also observe T == true. Suggested-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: umgwanakikbuti@gmail.com Cc: ktkhai@parallels.com Cc: rostedt@goodmis.org Cc: juri.lelli@gmail.com Cc: pang.xunlei@linaro.org Cc: oleg@redhat.com Cc: wanpeng.li@linux.intel.com Cc: Al Viro <viro@ZenIV.linux.org.uk> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20150617122924.GP3644@twins.programming.kicks-ass.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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File | Mode | Size |
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Kconfig | -rw-r--r-- | 3.7 KB |
Kconfig.iosched | -rw-r--r-- | 1.6 KB |
Makefile | -rw-r--r-- | 923 bytes |
bio-integrity.c | -rw-r--r-- | 14.0 KB |
bio.c | -rw-r--r-- | 49.4 KB |
blk-cgroup.c | -rw-r--r-- | 29.6 KB |
blk-cgroup.h | -rw-r--r-- | 16.6 KB |
blk-core.c | -rw-r--r-- | 90.1 KB |
blk-exec.c | -rw-r--r-- | 3.5 KB |
blk-flush.c | -rw-r--r-- | 14.8 KB |
blk-integrity.c | -rw-r--r-- | 12.4 KB |
blk-ioc.c | -rw-r--r-- | 10.2 KB |
blk-iopoll.c | -rw-r--r-- | 5.8 KB |
blk-lib.c | -rw-r--r-- | 8.0 KB |
blk-map.c | -rw-r--r-- | 5.2 KB |
blk-merge.c | -rw-r--r-- | 14.5 KB |
blk-mq-cpu.c | -rw-r--r-- | 1.6 KB |
blk-mq-cpumap.c | -rw-r--r-- | 2.5 KB |
blk-mq-sysfs.c | -rw-r--r-- | 10.6 KB |
blk-mq-tag.c | -rw-r--r-- | 15.4 KB |
blk-mq-tag.h | -rw-r--r-- | 2.1 KB |
blk-mq.c | -rw-r--r-- | 52.4 KB |
blk-mq.h | -rw-r--r-- | 3.3 KB |
blk-settings.c | -rw-r--r-- | 27.2 KB |
blk-softirq.c | -rw-r--r-- | 4.4 KB |
blk-sysfs.c | -rw-r--r-- | 15.5 KB |
blk-tag.c | -rw-r--r-- | 10.0 KB |
blk-throttle.c | -rw-r--r-- | 45.8 KB |
blk-timeout.c | -rw-r--r-- | 5.7 KB |
blk.h | -rw-r--r-- | 8.6 KB |
bounce.c | -rw-r--r-- | 6.5 KB |
bsg-lib.c | -rw-r--r-- | 6.0 KB |
bsg.c | -rw-r--r-- | 22.9 KB |
cfq-iosched.c | -rw-r--r-- | 120.3 KB |
cmdline-parser.c | -rw-r--r-- | 4.9 KB |
compat_ioctl.c | -rw-r--r-- | 20.8 KB |
deadline-iosched.c | -rw-r--r-- | 11.3 KB |
elevator.c | -rw-r--r-- | 23.7 KB |
genhd.c | -rw-r--r-- | 44.3 KB |
ioctl.c | -rw-r--r-- | 10.7 KB |
ioprio.c | -rw-r--r-- | 5.0 KB |
noop-iosched.c | -rw-r--r-- | 2.7 KB |
partition-generic.c | -rw-r--r-- | 14.0 KB |
scsi_ioctl.c | -rw-r--r-- | 19.4 KB |
t10-pi.c | -rw-r--r-- | 5.1 KB |
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