Messages in this thread | | | Date | Mon, 2 Mar 2009 14:13:13 +0100 | From | Jens Axboe <> | Subject | Re: The difference of request dir between AS and Deadline I/O scheduler? |
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On Mon, Mar 02 2009, ???? wrote: > Do you mean that the same process tends to have the same behavior of > I/O in the way of sycn? > Does this mean AS works better when requests are distincted by sync > mode (the success rate of anticipation is higher when requests are > grouped by the mode of sync)?
Please don't top post, put your reply beneath the text you are replying to.
It means that there's a key distinction between requests. Sync requests often have dependencies on each other, and AS thus enables idling for these types of requests. Async io is usually background activity. I don't understand what you mean by higher success rate. Anticipation is only for sync requests. The grouping is done because it makes behavioural sense.
> > Thanks, > > > On Mon, Mar 2, 2009 at 8:25 PM, Jens Axboe <jens.axboe@oracle.com> wrote: > > On Mon, Mar 02 2009, ???? wrote: > >> Hi, > >> > >> I'm little confused about the defination of request dir in AS and > >> Deadline I/O scheduler. > >> In AS, the request dir is defined by wheher it's sync: > >> > >> data_dir = rq_is_sync(rq); > >> > >> But in Deadline, the requests are grouped by read and write. > >> > >> Why is there the difference since AS is an extension of Deadline? > >> what's the consideration? > > > > Because AS uses the sync vs async distinction to decide whether to > > anticipate a new request from that process. 'sync' is then reads or sync > > writes, whereas deadline does not distinguish between sync and async > > writes. > > > > -- > > Jens Axboe > > > > > > > > -- > Xie Gang
-- Jens Axboe
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