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Date: Mon, 30 Apr 2012 23:03:23 -0700 From: George Porter <gmporter@...ucsd.edu> To: linux-kernel@...r.kernel.org Subject: read() syscall slowing down due to other threads? Hi all, I've run into a weird phenomenon I was hoping someone could help me pin down. I've got a multithreaded program which reads data off of 8 input disks, and does some processing on it. I have 8 Reader threads, each of which reads data off of one of the eight input disks. That data gets passed to other threads, which do some processing (this is an 8 core machine). If I do no or minimal processing in those other threads, the read() calls go at the speed of the disks (~100 MBps). I measure that speed by taking a timestamp before the read syscall, then afterwards, and dividing that into the read size (5MB). All seems good. However, if I start doing more computation on those other threads, the read() syscalls take longer to read the same amount of data, eventually slowing down to 50 MBps (50% slower). I've used setaffinity() to isolate the Reader threads to one set of cores, and the compute threads to a different set of cores, and so I don't think it is CPU/scheduling interference. Thoughts? Has anyone run into this before? Also, if you could CC me directly on any responses I would appreciate it. Thanks, George -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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