From 938ece711c5b1ba4fa8e3b9fc8cc03843ae82a5b Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sun, 6 Jul 2014 16:39:26 +0200 Subject: virtio-scsi: replace target spinlock with seqcount The spinlock of tgt_lock is only for serializing read and write req_vq, one lockless seqcount is enough for the purpose. On one 16core VM with vhost-scsi backend, the patch can improve IOPS with 3% on random read test. Signed-off-by: Ming Lei [Add initialization in virtscsi_target_alloc. - Paolo] Signed-off-by: Paolo Bonzini Signed-off-by: Christoph Hellwig --- drivers/scsi/virtio_scsi.c | 42 +++++++++++++++++++++++++++++------------- 1 file changed, 29 insertions(+), 13 deletions(-) (limited to 'drivers/scsi/virtio_scsi.c') diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index 308256b5e4cb..cdce502c3c46 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -27,6 +27,7 @@ #include #include #include +#include #define VIRTIO_SCSI_MEMPOOL_SZ 64 #define VIRTIO_SCSI_EVENT_LEN 8 @@ -75,18 +76,16 @@ struct virtio_scsi_vq { * queue, and also lets the driver optimize the IRQ affinity for the virtqueues * (each virtqueue's affinity is set to the CPU that "owns" the queue). * - * tgt_lock is held to serialize reading and writing req_vq. Reading req_vq - * could be done locklessly, but we do not do it yet. + * tgt_seq is held to serialize reading and writing req_vq. * * Decrements of reqs are never concurrent with writes of req_vq: before the * decrement reqs will be != 0; after the decrement the virtqueue completion * routine will not use the req_vq so it can be changed by a new request. - * Thus they can happen outside the tgt_lock, provided of course we make reqs + * Thus they can happen outside the tgt_seq, provided of course we make reqs * an atomic_t. */ struct virtio_scsi_target_state { - /* This spinlock never held at the same time as vq_lock. */ - spinlock_t tgt_lock; + seqcount_t tgt_seq; /* Count of outstanding requests. */ atomic_t reqs; @@ -559,19 +558,33 @@ static struct virtio_scsi_vq *virtscsi_pick_vq(struct virtio_scsi *vscsi, unsigned long flags; u32 queue_num; - spin_lock_irqsave(&tgt->tgt_lock, flags); + local_irq_save(flags); + if (atomic_inc_return(&tgt->reqs) > 1) { + unsigned long seq; + + do { + seq = read_seqcount_begin(&tgt->tgt_seq); + vq = tgt->req_vq; + } while (read_seqcount_retry(&tgt->tgt_seq, seq)); + } else { + /* no writes can be concurrent because of atomic_t */ + write_seqcount_begin(&tgt->tgt_seq); + + /* keep previous req_vq if a reader just arrived */ + if (unlikely(atomic_read(&tgt->reqs) > 1)) { + vq = tgt->req_vq; + goto unlock; + } - if (atomic_inc_return(&tgt->reqs) > 1) - vq = tgt->req_vq; - else { queue_num = smp_processor_id(); while (unlikely(queue_num >= vscsi->num_queues)) queue_num -= vscsi->num_queues; - tgt->req_vq = vq = &vscsi->req_vqs[queue_num]; + unlock: + write_seqcount_end(&tgt->tgt_seq); } + local_irq_restore(flags); - spin_unlock_irqrestore(&tgt->tgt_lock, flags); return vq; } @@ -667,14 +680,17 @@ static int virtscsi_abort(struct scsi_cmnd *sc) static int virtscsi_target_alloc(struct scsi_target *starget) { + struct Scsi_Host *sh = dev_to_shost(starget->dev.parent); + struct virtio_scsi *vscsi = shost_priv(sh); + struct virtio_scsi_target_state *tgt = kmalloc(sizeof(*tgt), GFP_KERNEL); if (!tgt) return -ENOMEM; - spin_lock_init(&tgt->tgt_lock); + seqcount_init(&tgt->tgt_seq); atomic_set(&tgt->reqs, 0); - tgt->req_vq = NULL; + tgt->req_vq = &vscsi->req_vqs[0]; starget->hostdata = tgt; return 0; -- cgit v1.2.3 From 761f1193f299873236dbc21277864d70cb7ba8a3 Mon Sep 17 00:00:00 2001 From: Venkatesh Srinivas Date: Sun, 6 Jul 2014 16:39:27 +0200 Subject: virtio-scsi: Implement change_queue_depth for virtscsi targets change_queue_depth allows changing per-target queue depth via sysfs. It also allows the SCSI midlayer to ramp down the number of concurrent inflight requests in response to a SCSI BUSY status response and allows the midlayer to ramp the count back up to the device maximum when the BUSY condition has resolved. Signed-off-by: Venkatesh Srinivas Signed-off-by: Paolo Bonzini Signed-off-by: Christoph Hellwig --- drivers/scsi/virtio_scsi.c | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'drivers/scsi/virtio_scsi.c') diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index cdce502c3c46..eee1bc0b506e 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #define VIRTIO_SCSI_MEMPOOL_SZ 64 @@ -654,6 +655,36 @@ static int virtscsi_device_reset(struct scsi_cmnd *sc) return virtscsi_tmf(vscsi, cmd); } +/** + * virtscsi_change_queue_depth() - Change a virtscsi target's queue depth + * @sdev: Virtscsi target whose queue depth to change + * @qdepth: New queue depth + * @reason: Reason for the queue depth change. + */ +static int virtscsi_change_queue_depth(struct scsi_device *sdev, + int qdepth, + int reason) +{ + struct Scsi_Host *shost = sdev->host; + int max_depth = shost->cmd_per_lun; + + switch (reason) { + case SCSI_QDEPTH_QFULL: /* Drop qdepth in response to BUSY state */ + scsi_track_queue_full(sdev, qdepth); + break; + case SCSI_QDEPTH_RAMP_UP: /* Raise qdepth after BUSY state resolved */ + case SCSI_QDEPTH_DEFAULT: /* Manual change via sysfs */ + scsi_adjust_queue_depth(sdev, + scsi_get_tag_type(sdev), + min(max_depth, qdepth)); + break; + default: + return -EOPNOTSUPP; + } + + return sdev->queue_depth; +} + static int virtscsi_abort(struct scsi_cmnd *sc) { struct virtio_scsi *vscsi = shost_priv(sc->device->host); @@ -709,6 +740,7 @@ static struct scsi_host_template virtscsi_host_template_single = { .this_id = -1, .cmd_size = sizeof(struct virtio_scsi_cmd), .queuecommand = virtscsi_queuecommand_single, + .change_queue_depth = virtscsi_change_queue_depth, .eh_abort_handler = virtscsi_abort, .eh_device_reset_handler = virtscsi_device_reset, @@ -726,6 +758,7 @@ static struct scsi_host_template virtscsi_host_template_multi = { .this_id = -1, .cmd_size = sizeof(struct virtio_scsi_cmd), .queuecommand = virtscsi_queuecommand_multi, + .change_queue_depth = virtscsi_change_queue_depth, .eh_abort_handler = virtscsi_abort, .eh_device_reset_handler = virtscsi_device_reset, -- cgit v1.2.3