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Date: Sun, 05 Jul 2009 12:27:01 +0300
From: Boaz Harrosh <bharrosh@...asas.com>
To: Tejun Heo <tj@...nel.org>
CC: Jens Axboe <jens.axboe@...cle.com>,
Linux Kernel <linux-kernel@...r.kernel.org>,
James Bottomley <James.Bottomley@...senPartnership.com>,
linux-scsi <linux-scsi@...r.kernel.org>,
Niel Lambrechts <niel.lambrechts@...il.com>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 2/4] block: use the same failfast bits for bio and request
On 07/03/2009 11:48 AM, Tejun Heo wrote:
> bio and request use the same set of failfast bits. This patch makes
> the following changes to simplify things.
>
> * enumify BIO_RW* bits and reorder bits such that BIOS_RW_FAILFAST_*
> bits coincide with __REQ_FAILFAST_* bits.
>
> * The above pushes BIO_RW_AHEAD out of sync with __REQ_FAILFAST_DEV
> but the matching is useless anyway. init_request_from_bio() is
> responsible for setting FAILFAST bits on FS requests and non-FS
> requests never use BIO_RW_AHEAD. Drop the code and comment from
> blk_rq_bio_prep().
>
> * Define REQ_FAILFAST_MASK which is OR of all FAILFAST bits and
> simplify FAILFAST flags handling in init_request_from_bio().
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Jens Axboe <axboe@...nel.dk>
Hi Tejun.
Thanks for doing this, it has been neglected for a long time.
However, it will happen again, I don't like these implicit matches
which are not enforced, They get to drift away. There are several ways
to make sure two sets of enums stay in sync. (I'll have a try at it
tomorrow. if you want).
> ---
> block/blk-core.c | 19 +++++++------------
> include/linux/bio.h | 43 +++++++++++++++++++++++--------------------
> include/linux/blkdev.h | 4 ++++
> 3 files changed, 34 insertions(+), 32 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 8f4b9e0..cd3b265 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1119,17 +1119,13 @@ void init_request_from_bio(struct request *req, struct bio *bio)
> req->cmd_type = REQ_TYPE_FS;
>
> /*
> - * inherit FAILFAST from bio (for read-ahead, and explicit FAILFAST)
> + * Inherit FAILFAST from bio (for read-ahead, and explicit
> + * FAILFAST). FAILFAST flags are identical for req and bio.
> */
> if (bio_rw_ahead(bio))
> - req->cmd_flags |= (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT |
> - REQ_FAILFAST_DRIVER);
> - if (bio_failfast_dev(bio))
> - req->cmd_flags |= REQ_FAILFAST_DEV;
> - if (bio_failfast_transport(bio))
> - req->cmd_flags |= REQ_FAILFAST_TRANSPORT;
> - if (bio_failfast_driver(bio))
> - req->cmd_flags |= REQ_FAILFAST_DRIVER;
> + req->cmd_flags |= REQ_FAILFAST_MASK;
> + else
> + req->cmd_flags |= bio->bi_rw & REQ_FAILFAST_MASK;
>
> if (unlikely(bio_discard(bio))) {
> req->cmd_flags |= REQ_DISCARD;
> @@ -2247,9 +2243,8 @@ EXPORT_SYMBOL_GPL(__blk_end_request_cur);
> void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
> struct bio *bio)
> {
> - /* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw, and
> - we want BIO_RW_AHEAD (bit 1) to imply REQ_FAILFAST (bit 1). */
> - rq->cmd_flags |= (bio->bi_rw & 3);
> + /* Bit 0 (R/W) is identical in rq->cmd_flags and bio->bi_rw */
> + rq->cmd_flags |= bio->bi_rw & REQ_RW;
>
> if (bio_has_data(bio)) {
> rq->nr_phys_segments = bio_phys_segments(q, bio);
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index 2892b71..a299ed3 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -142,37 +142,40 @@ struct bio {
> *
> * bit 0 -- data direction
> * If not set, bio is a read from device. If set, it's a write to device.
> - * bit 1 -- rw-ahead when set
> - * bit 2 -- barrier
> + * bit 1 -- fail fast device errors
> + * bit 2 -- fail fast transport errors
> + * bit 3 -- fail fast driver errors
> + * bit 4 -- rw-ahead when set
> + * bit 5 -- barrier
Please kill all these evil bit 1, bit 2 ,bit n comments. The ways we
invent to torture ourselfs...
Just move all the comments to the enums declarations below. And be done
with it, also for the next time.
> * Insert a serialization point in the IO queue, forcing previously
> * submitted IO to be completed before this one is issued.
> - * bit 3 -- synchronous I/O hint.
> - * bit 4 -- Unplug the device immediately after submitting this bio.
> - * bit 5 -- metadata request
> + * bit 6 -- synchronous I/O hint.
> + * bit 7 -- Unplug the device immediately after submitting this bio.
> + * bit 8 -- metadata request
> * Used for tracing to differentiate metadata and data IO. May also
> * get some preferential treatment in the IO scheduler
> - * bit 6 -- discard sectors
> + * bit 9 -- discard sectors
> * Informs the lower level device that this range of sectors is no longer
> * used by the file system and may thus be freed by the device. Used
> * for flash based storage.
> - * bit 7 -- fail fast device errors
> - * bit 8 -- fail fast transport errors
> - * bit 9 -- fail fast driver errors
> * Don't want driver retries for any fast fail whatever the reason.
> * bit 10 -- Tell the IO scheduler not to wait for more requests after this
> one has been submitted, even if it is a SYNC request.
> */
> -#define BIO_RW 0 /* Must match RW in req flags (blkdev.h) */
> -#define BIO_RW_AHEAD 1 /* Must match FAILFAST in req flags */
> -#define BIO_RW_BARRIER 2
> -#define BIO_RW_SYNCIO 3
> -#define BIO_RW_UNPLUG 4
> -#define BIO_RW_META 5
> -#define BIO_RW_DISCARD 6
> -#define BIO_RW_FAILFAST_DEV 7
> -#define BIO_RW_FAILFAST_TRANSPORT 8
> -#define BIO_RW_FAILFAST_DRIVER 9
> -#define BIO_RW_NOIDLE 10
> +enum bio_rw_flags {
> + BIO_RW,
> + BIO_RW_FAILFAST_DEV,
> + BIO_RW_FAILFAST_TRANSPORT,
> + BIO_RW_FAILFAST_DRIVER,
> + /* above flags must match REQ_* */
> + BIO_RW_AHEAD,
> + BIO_RW_BARRIER,
> + BIO_RW_SYNCIO,
> + BIO_RW_UNPLUG,
> + BIO_RW_META,
> + BIO_RW_DISCARD,
> + BIO_RW_NOIDLE,
> +};
>
> #define bio_rw_flagged(bio, flag) ((bio)->bi_rw & (1 << (flag)))
>
I wish there was also an helper to set these bits. it gives me an heart attack
every time I need to:
bio->bi_rw &= ~(1 << BIO_RW);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 49ae079..a0e5ce1 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -98,6 +98,7 @@ enum rq_flag_bits {
> __REQ_FAILFAST_DEV, /* no driver retries of device errors */
> __REQ_FAILFAST_TRANSPORT, /* no driver retries of transport errors */
> __REQ_FAILFAST_DRIVER, /* no driver retries of driver errors */
> + /* above flags must match BIO_RW_* */
> __REQ_DISCARD, /* request to discard sectors */
> __REQ_SORTED, /* elevator knows about this request */
> __REQ_SOFTBARRIER, /* may not be passed by ioscheduler */
> @@ -148,6 +149,9 @@ enum rq_flag_bits {
> #define REQ_NOIDLE (1 << __REQ_NOIDLE)
> #define REQ_IO_STAT (1 << __REQ_IO_STAT)
>
> +#define REQ_FAILFAST_MASK (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | \
> + REQ_FAILFAST_DRIVER)
> +
> #define BLK_MAX_CDB 16
>
> /*
Thanks
Boaz
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