lkml.org 
[lkml]   [2011]   [Mar]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH 04/10] block: initial patch for on-stack per-task plugging
    From
    2011/1/22 Jens Axboe <jaxboe@fusionio.com>:
    > Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
    > ---
    >  block/blk-core.c          |  357 ++++++++++++++++++++++++++++++++------------
    >  block/elevator.c          |    6 +-
    >  include/linux/blk_types.h |    2 +
    >  include/linux/blkdev.h    |   30 ++++
    >  include/linux/elevator.h  |    1 +
    >  include/linux/sched.h     |    6 +
    >  kernel/exit.c             |    1 +
    >  kernel/fork.c             |    3 +
    >  kernel/sched.c            |   11 ++-
    >  9 files changed, 317 insertions(+), 100 deletions(-)
    >
    > diff --git a/block/blk-core.c b/block/blk-core.c
    > index 960f12c..42dbfcc 100644
    > --- a/block/blk-core.c
    > +++ b/block/blk-core.c
    > @@ -27,6 +27,7 @@
    >  #include <linux/writeback.h>
    >  #include <linux/task_io_accounting_ops.h>
    >  #include <linux/fault-inject.h>
    > +#include <linux/list_sort.h>
    >
    >  #define CREATE_TRACE_POINTS
    >  #include <trace/events/block.h>
    > @@ -213,7 +214,7 @@ static void blk_delay_work(struct work_struct *work)
    >
    >        q = container_of(work, struct request_queue, delay_work.work);
    >        spin_lock_irq(q->queue_lock);
    > -       q->request_fn(q);
    > +       __blk_run_queue(q);
    >        spin_unlock_irq(q->queue_lock);
    >  }
    Hi Jens,
    I have some questions about the per-task plugging. Since the request
    list is per-task, and each task delivers its requests at finish flush
    or schedule. But when one cpu delivers requests to global queue, other
    cpus don't know. This seems to have problem. For example:
    1. get_request_wait() can only flush current task's request list,
    other cpus/tasks might still have a lot of requests, which aren't sent
    to request_queue. your ioc-rq-alloc branch is for this, right? Will it
    be pushed to 2.6.39 too? I'm wondering if we should limit per-task
    queue length. If there are enough requests there, we force a flush
    plug.
    2. some APIs like blk_delay_work, which call __blk_run_queue() might
    not work. because other CPUs might not dispatch their requests to
    request queue. So __blk_run_queue will eventually find no requests,
    which might stall devices.
    Since one cpu doesn't know other cpus' request list, I'm wondering if
    there are other similar issues.

    Thanks,
    Shaohua
    --
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2011-03-16 09:21    [W:0.023 / U:90.032 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site