From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: NeilBrown <neilb-IBi9RG/b67k@public.gmane.org>
Cc: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org,
axboe-b10kYP2dOMg@public.gmane.org,
milosz-B5zB6C1i6pkAvxtiuMwx3w@public.gmane.org,
linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2
Date: Wed, 11 May 2016 10:55:20 +0200 [thread overview]
Message-ID: <20160511085520.GA20377@lst.de> (raw)
In-Reply-To: <874ma8usrr.fsf-wvvUuzkyo1HefUI2i7LXDhCRmIWqnp/j@public.gmane.org>
On Mon, May 09, 2016 at 07:47:04AM +1000, NeilBrown wrote:
> On Fri, Mar 04 2016, Christoph Hellwig wrote:
>
> > This adds a flag that tells the file system that this is a high priority
> > request for which it's worth to poll the hardware. The flag is purely
> > advisory and can be ignored if not supported.
>
> Here you say the flag is "advice".
>
> >
> > +/* flags for preadv2/pwritev2: */
> > +#define RWF_HIPRI 0x00000001 /* high priority request, poll if possible */
>
> This text makes it sound like a firm "request" ("if possible").
"request" here is in the sense of an I/O request. Better wording
highly welcome.
>
> > provides lower latency, but may use additional ressources
>
> Is this a "latency vs throughput" trade-off, or something more subtle?
> It would be nice to make the decision process as obvious as possible for
> the developer considering the use of this flag.
If you poll you can't do anything else, so you end up using CPU
cycles to wait which otherwise could do something productive.
next prev parent reply other threads:[~2016-05-11 8:55 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-03 15:03 generic RDMA READ/WRITE API V2 Christoph Hellwig
2016-03-03 15:03 ` [PATCH 2/6] vfs: vfs: Define new syscalls preadv2,pwritev2 Christoph Hellwig
2016-03-10 18:15 ` Michael Kerrisk (man-pages)
[not found] ` <56E1B9A8.3070904-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2016-03-11 9:53 ` Christoph Hellwig
[not found] ` <20160311095357.GA29350-jcswGhMUV9g@public.gmane.org>
2016-04-18 13:51 ` Michael Kerrisk (man-pages)
[not found] ` <5714E676.4090007-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2016-04-25 8:47 ` Christoph Hellwig
[not found] ` <20160425084715.GA29255-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2016-04-25 17:35 ` Michael Kerrisk (man-pages)
2016-05-08 9:29 ` Christoph Hellwig
[not found] ` <1457017443-17662-1-git-send-email-hch-jcswGhMUV9g@public.gmane.org>
2016-03-03 15:03 ` [PATCH 1/6] vfs: pass a flags argument to vfs_readv/vfs_writev Christoph Hellwig
2016-03-03 15:04 ` [PATCH 3/6] x86: wire up preadv2 and pwritev2 Christoph Hellwig
2016-03-03 15:04 ` [PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2 Christoph Hellwig
[not found] ` <1457017443-17662-5-git-send-email-hch-jcswGhMUV9g@public.gmane.org>
2016-05-08 21:47 ` NeilBrown
[not found] ` <874ma8usrr.fsf-wvvUuzkyo1HefUI2i7LXDhCRmIWqnp/j@public.gmane.org>
2016-05-11 8:55 ` Christoph Hellwig [this message]
2016-03-03 15:04 ` [PATCH 5/6] direct-io: only use block polling if explicitly requested Christoph Hellwig
2016-03-03 15:04 ` [PATCH 6/6] blk-mq: enable polling support by default Christoph Hellwig
2016-03-03 15:09 ` generic RDMA READ/WRITE API V2 Sagi Grimberg
2016-03-03 15:11 ` selective block polling and preadv2/pwritev2 revisited V3 Christoph Hellwig
2016-03-03 15:16 ` Jens Axboe
[not found] ` <20160303151116.GA24614-jcswGhMUV9g@public.gmane.org>
2016-03-03 15:52 ` Arnd Bergmann
2016-03-03 16:11 ` Christoph Hellwig
-- strict thread matches above, loose matches on Subject: below --
2015-12-24 14:14 selective block polling and preadv2/pwritev2 revisited Christoph Hellwig
2015-12-24 14:14 ` [PATCH 4/6] vfs: add the RWF_HIPRI flag for preadv2/pwritev2 Christoph Hellwig
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