Re: [PATCH v3 01/18] block: introduce duration-limits priority class

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On 1/28/23 19:52, Damien Le Moal wrote:
+/*
+ * The 13-bits of ioprio data for each class provide up to 8 QOS hints and
+ * up to 8 priority levels.
+ */
+#define IOPRIO_PRIO_LEVEL_MASK	(IOPRIO_NR_LEVELS - 1)
+#define IOPRIO_QOS_HINT_SHIFT	10
+#define IOPRIO_NR_QOS_HINTS	8
+#define IOPRIO_QOS_HINT_MASK	(IOPRIO_NR_QOS_HINTS - 1)
+#define IOPRIO_PRIO_LEVEL(ioprio)	((ioprio) & IOPRIO_PRIO_LEVEL_MASK)
+#define IOPRIO_QOS_HINT(ioprio)	\
+	(((ioprio) >> IOPRIO_QOS_HINT_SHIFT) & IOPRIO_QOS_HINT_MASK)

Does the QoS level really have to be encoded in bio.bi_ioprio? How about introducing a new field in the existing hole in struct bio? From the pahole output:

struct bio {
        struct bio *               bi_next;            /*     0     4 */
        struct block_device *      bi_bdev;            /*     4     4 */
        blk_opf_t                  bi_opf;             /*     8     4 */
        short unsigned int         bi_flags;           /*    12     2 */
        short unsigned int         bi_ioprio;          /*    14     2 */
        blk_status_t               bi_status;          /*    16     1 */

        /* XXX 3 bytes hole, try to pack */

        atomic_t                   __bi_remaining;     /*    20     4 */
        struct bvec_iter           bi_iter;            /*    24    20 */
        blk_qc_t                   bi_cookie;          /*    44     4 */
        bio_end_io_t *             bi_end_io;          /*    48     4 */
        void *                     bi_private;         /*    52     4 */
        struct bio_crypt_ctx *     bi_crypt_context;   /*    56     4 */
[ ... ]

Thanks,

Bart.



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