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Linux 3.16: Deadline I/O Scheduler Generally Leads With A SSD

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  • stqn
    replied
    Would it change something to the results to add the discard option? I think that?s how most people mount their SSDs under Linux?

    Besides it looks like deadline only wins on synthetic benchmarks.

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  • Caleb
    replied
    Can you also test BFQ in the future? After all, work is being done right now to integrate it into the kernel, and it's also supposed to replace CFQ when that happens.

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  • a user
    replied
    Originally posted by xeekei View Post
    This is interesting, I seem to recall Noop being the fastest on SSDs? I might need to change my Udev rule now.
    deadline always was the better io schedular, at least for ssds.

    Leave a comment:


  • elbar
    replied
    benchmark

    What about some other benchmark. Like destroying SSD, HDD or something.

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  • oneofone
    replied
    Originally posted by rohcQaH View Post
    These benchmarks measure throughput, but not responsiveness under load. Someone only interested in throughput will find the benchmark results helpful. If responsiveness is required, more research would be needed - from their implementations, I'd expect CFQ to better at that, but I have no data to back it up.
    No scientific data to back my claim, but with 3 good ol' SATA 5 -year-old HDDs, I've tried cfq, bfq (with and without the bfs) and noop, deadline is by far the most responsive under load.

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  • rohcQaH
    replied
    These benchmarks measure throughput, but not responsiveness under load. Someone only interested in throughput will find the benchmark results helpful. If responsiveness is required, more research would be needed - from their implementations, I'd expect CFQ to better at that, but I have no data to back it up.

    Leave a comment:


  • Alejandro Nova
    replied
    Originally posted by xeekei View Post
    It seems so. It's possible to write a udev rule that detects if it's a rotational medium or solid state, and set the scheduler accordingly. I have Noop for SSDs and CFQ for HDDs. I think it will choose Noop for USB thumbsticks and the like too.
    Code:
    [[email protected] ~]# cat /etc/udev/rules.d/60-io_schedulers.rules 
    # Set deadline scheduler for non-rotating disks
    ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/scheduler}="deadline"
    ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="0", ATTR{queue/iosched/fifo_batch}="1"
    # Set cfq scheduler for rotating disks
    ACTION=="add|change", KERNEL=="sd[a-z]", ATTR{queue/rotational}=="1", ATTR{queue/scheduler}="cfq"
    That's better. Pay attention to the line coming after the "deadline" setting, that line improves performance even more

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  • justanarcher
    replied
    CFQ is supposedly already tweaked for SSDs.

    From https://www.kernel.org/doc/Documenta...fq-iosched.txt

    CFQ has some optimizations for SSDs and if it detects a non-rotational
    media which can support higher queue depth (multiple requests at in
    flight at a time), then it cuts down on idling of individual queues and
    all the queues move to sync-noidle tree and only tree idle remains. This
    tree idling provides isolation with buffered write queues on async tree.

    Leave a comment:


  • ferry
    replied
    I have a eepc notebook with extremely slow SSD. What I've noted over the years is that I don't really care how fast the disk is, but whether or now the desktop remains responsive when a backgroud process is pounding the disk. Typically, can I continue web browsing while synaptic/apt is updating packages?

    In the above scenario I've noted that changing scheduling and priority for synaptic and children had a large effect. Also note that on the same machine with windows xp while starting firefox/thunderbird the machine, even the mouse pointer freezes for 10 - 30 sec. (due to long stall caused by windows fsync equivalent), while doing the same on Linux is workable.

    I wonder if such a scenario if sufficiently convered by the bench marks.

    Leave a comment:


  • xeekei
    replied
    Originally posted by peppercats View Post
    so if I only use an SSD I should switch to deadline?
    It seems so. It's possible to write a udev rule that detects if it's a rotational medium or solid state, and set the scheduler accordingly. I have Noop for SSDs and CFQ for HDDs. I think it will choose Noop for USB thumbsticks and the like too.

    Leave a comment:

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