> HI Neil, > > thanks for the explanations. I tried to understand the reason for the > "bad" benchmark numbers during my direct IO write tests for my rmw > patch. I only choose it to avoid caching side effects. Even with 64 > threads there is still a large gap to the theoretical maximum. So I > reduced the test to 1 writer and took some time to have a look how > raid5.c handles sync/direct writes. See my other post with only 5MB/s > 4K direct writes to ramdisk backed raid5 md. > > With that insight I started to compare it to raid1.c. After some > iterations it came to my mind that the empty raid5d() runs between > two sync writes might give extra latency and so I looked for corners > where md_wakeup_thread() might be unnecessary. The result are > the questions above. > > I'll give the clear_bit(THREAD_WAKEUP,...) a try. > > Markus Just an all-clear response. The error I was analyzing came from my Virutalbox test environment. With more than one CPU activated process synchronzation seems to face high synchonization penalties between make_request() and raid5d(). Switching back to real hardware with /dev/ramX shows normal throughput. A lot to wonder about when testing the kernel ... Markus
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