Michael S. Tsirkin
2021-Sep-09 22:57 UTC
[PATCH v2 1/1] virtio-blk: add num_io_queues module parameter
On Thu, Sep 09, 2021 at 07:45:42PM +0300, Max Gurtovoy wrote:> > On 9/9/2021 7:31 PM, Michael S. Tsirkin wrote: > > On Thu, Sep 09, 2021 at 06:51:56PM +0300, Max Gurtovoy wrote: > > > On 9/9/2021 6:40 PM, Michael S. Tsirkin wrote: > > > > On Thu, Sep 09, 2021 at 06:37:37PM +0300, Max Gurtovoy wrote: > > > > > On 9/9/2021 4:42 PM, Michael S. Tsirkin wrote: > > > > > > On Mon, Sep 06, 2021 at 02:59:40PM +0300, Max Gurtovoy wrote: > > > > > > > On 9/6/2021 2:20 PM, Michael S. Tsirkin wrote: > > > > > > > > On Mon, Sep 06, 2021 at 01:31:32AM +0300, Max Gurtovoy wrote: > > > > > > > > > On 9/5/2021 7:02 PM, Michael S. Tsirkin wrote: > > > > > > > > > > On Thu, Sep 02, 2021 at 02:45:52PM +0100, Stefan Hajnoczi wrote: > > > > > > > > > > > On Tue, Aug 31, 2021 at 04:50:35PM +0300, Max Gurtovoy wrote: > > > > > > > > > > > > Sometimes a user would like to control the amount of IO queues to be > > > > > > > > > > > > created for a block device. For example, for limiting the memory > > > > > > > > > > > > footprint of virtio-blk devices. > > > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Max Gurtovoy <mgurtovoy at nvidia.com> > > > > > > > > > > > > --- > > > > > > > > > > > > > > > > > > > > > > > > changes from v1: > > > > > > > > > > > > - use param_set_uint_minmax (from Christoph) > > > > > > > > > > > > - added "Should > 0" to module description > > > > > > > > > > > > > > > > > > > > > > > > Note: This commit apply on top of Jens's branch for-5.15/drivers > > > > > > > > > > > > --- > > > > > > > > > > > > drivers/block/virtio_blk.c | 20 +++++++++++++++++++- > > > > > > > > > > > > 1 file changed, 19 insertions(+), 1 deletion(-) > > > > > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > > > > > > > > > > > > index 4b49df2dfd23..9332fc4e9b31 100644 > > > > > > > > > > > > --- a/drivers/block/virtio_blk.c > > > > > > > > > > > > +++ b/drivers/block/virtio_blk.c > > > > > > > > > > > > @@ -24,6 +24,22 @@ > > > > > > > > > > > > /* The maximum number of sg elements that fit into a virtqueue */ > > > > > > > > > > > > #define VIRTIO_BLK_MAX_SG_ELEMS 32768 > > > > > > > > > > > > +static int virtblk_queue_count_set(const char *val, > > > > > > > > > > > > + const struct kernel_param *kp) > > > > > > > > > > > > +{ > > > > > > > > > > > > + return param_set_uint_minmax(val, kp, 1, nr_cpu_ids); > > > > > > > > > > > > +} > > > > > > > > Hmm which tree is this for? > > > > > > > I've mentioned in the note that it apply on branch for-5.15/drivers. But now > > > > > > > you can apply it on linus/master as well. > > > > > > > > > > > > > > > > > > > > > > > > > > + > > > > > > > > > > > > +static const struct kernel_param_ops queue_count_ops = { > > > > > > > > > > > > + .set = virtblk_queue_count_set, > > > > > > > > > > > > + .get = param_get_uint, > > > > > > > > > > > > +}; > > > > > > > > > > > > + > > > > > > > > > > > > +static unsigned int num_io_queues; > > > > > > > > > > > > +module_param_cb(num_io_queues, &queue_count_ops, &num_io_queues, 0644); > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_queues, > > > > > > > > > > > > + "Number of IO virt queues to use for blk device. Should > 0"); > > > > > > > > better: > > > > > > > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues, > > > > > > > > + "Limit number of IO request virt queues to use for each device. 0 for now limit"); > > > > > > > You proposed it and I replied on it bellow. > > > > > > Can't say I understand 100% what you are saying. Want to send > > > > > > a description that does make sense to you but > > > > > > also reflects reality? 0 is the default so > > > > > > "should > 0" besides being ungrammatical does not seem t" > > > > > > reflect what it does ... > > > > > if you "modprobe virtio_blk" the previous behavior will happen. > > > > > > > > > > You can't "modprobe virtio_blk num_io_request_queues=0" since the minimal > > > > > value is 1. > > > > > > > > > > So your description is not reflecting the code. > > > > > > > > > > We can do: > > > > > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to use for blk device. Minimum value is 1 queue"); > > > > What's the default value? We should document that. > > > default value for static global variables is 0. > > > > > > MODULE_PARM_DESC(num_io_request_queues, "Number of request virt queues to > > > use for blk device. Minimum value is 1 queue. Default and Maximum value is > > > equal to the total number of CPUs"); > > So it says it's the # of cpus but yoiu inspect it with > > sysfs and it's actually 0. Let's say that's confusing > > at the least. why not just let users set it to 0 > > and document that? > > > Setting it by the user to 0 makes no sense. > > We can say "if not set, the value equals to the total number of CPUs".the value is 0. it seems to mean "no limit". the actual # of queues is then te smaller between # of cpus and # of hardware queues. I see no reason not to allow user to set that especially if it was originally the value then user changed it and is trying to change it back.> The actual value of the created queues can be seen in /sys/block/vda/mq/ as > done today.> > > > > > > > > > > > + > > > > > > > > > > > > static int major; > > > > > > > > > > > > static DEFINE_IDA(vd_index_ida); > > > > > > > > > > > > @@ -501,7 +517,9 @@ static int init_vq(struct virtio_blk *vblk) > > > > > > > > > > > > if (err) > > > > > > > > > > > > num_vqs = 1; > > > > > > > > > > > > - num_vqs = min_t(unsigned int, nr_cpu_ids, num_vqs); > > > > > > > > > > > > + num_vqs = min_t(unsigned int, > > > > > > > > > > > > + min_not_zero(num_io_queues, nr_cpu_ids), > > > > > > > > > > > > + num_vqs); > > > > > > > > > > > If you respin, please consider calling them request queues. That's the > > > > > > > > > > > terminology from the VIRTIO spec and it's nice to keep it consistent. > > > > > > > > > > > But the purpose of num_io_queues is clear, so: > > > > > > > > > > > > > > > > > > > > > > Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com> > > > > > > > > > > I did this: > > > > > > > > > > +static unsigned int num_io_request_queues; > > > > > > > > > > +module_param_cb(num_io_request_queues, &queue_count_ops, &num_io_request_queues, 0644); > > > > > > > > > > +MODULE_PARM_DESC(num_io_request_queues, > > > > > > > > > > + "Limit number of IO request virt queues to use for each device. 0 for now limit"); > > > > > > > > > The parameter is writable and can be changed and then new devices might be > > > > > > > > > probed with new value. > > > > > > > > > > > > > > > > > > It can't be zero in the code. we can change param_set_uint_minmax args and > > > > > > > > > say that 0 says nr_cpus. > > > > > > > > > > > > > > > > > > I'm ok with the renaming but I prefer to stick to the description we gave in > > > > > > > > > V3 of this patch (and maybe enable value of 0 as mentioned above).