Messages in this thread | | | Date | Tue, 16 Jun 2015 11:28:11 +0800 | From | juncheng bai <> | Subject | Re: [PATCH RFC] storage:rbd: make the size of request is equal to the, size of the object |
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On 2015/6/15 22:27, Ilya Dryomov wrote: > On Mon, Jun 15, 2015 at 4:23 PM, juncheng bai > <baijuncheng@unitedstack.com> wrote: >> >> >> On 2015/6/15 21:03, Ilya Dryomov wrote: >>> >>> On Mon, Jun 15, 2015 at 2:18 PM, juncheng bai >>> <baijuncheng@unitedstack.com> wrote: >>>> >>>> From 6213215bd19926d1063d4e01a248107dab8a899b Mon Sep 17 00:00:00 2001 >>>> From: juncheng bai <baijuncheng@unitedstack.com> >>>> Date: Mon, 15 Jun 2015 18:34:00 +0800 >>>> Subject: [PATCH] storage:rbd: make the size of request is equal to the >>>> size of the object >>>> >>>> ensures that the merged size of request can achieve the size of >>>> the object. >>>> when merge a bio to request or merge a request to request, the >>>> sum of the segment number of the current request and the segment >>>> number of the bio is not greater than the max segments of the request, >>>> so the max size of request is 512k if the max segments of request is >>>> BLK_MAX_SEGMENTS. >>>> >>>> Signed-off-by: juncheng bai <baijuncheng@unitedstack.com> >>>> --- >>>> drivers/block/rbd.c | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c >>>> index 0a54c58..dec6045 100644 >>>> --- a/drivers/block/rbd.c >>>> +++ b/drivers/block/rbd.c >>>> @@ -3757,6 +3757,8 @@ static int rbd_init_disk(struct rbd_device >>>> *rbd_dev) >>>> segment_size = rbd_obj_bytes(&rbd_dev->header); >>>> blk_queue_max_hw_sectors(q, segment_size / SECTOR_SIZE); >>>> blk_queue_max_segment_size(q, segment_size); >>>> + if (segment_size > BLK_MAX_SEGMENTS * PAGE_SIZE) >>>> + blk_queue_max_segments(q, segment_size / PAGE_SIZE); >>>> blk_queue_io_min(q, segment_size); >>>> blk_queue_io_opt(q, segment_size); >>> >>> >>> I made a similar patch on Friday, investigating blk-mq plugging issue >>> reported by Nick. My patch sets it to BIO_MAX_PAGES unconditionally - >>> AFAIU there is no point in setting to anything bigger since the bios >>> will be clipped to that number of vecs. Given that BIO_MAX_PAGES is >>> 256, this gives is 1M direct I/Os. >> >> Hi. For signal bio, the max number of bio_vec is BIO_MAX_PAGES, but a >> request can be merged from multiple bios. We can see the below function: >> ll_back_merge_fn, ll_front_merge_fn and etc. >> And I test in kernel 3.18 use this patch, and do: >> echo 4096 > /sys/block/rbd0/queue/max_sectors_kb >> We use systemtap to trace the request size, It is upto 4M. > > Kernel 3.18 is pre rbd blk-mq transition, which happened in 4.0. You > should test whatever patches you have with at least 4.0. > > Putting that aside, I must be missing something. You'll get 4M > requests on 3.18 both with your patch and without it, the only > difference would be the size of bios being merged - 512k vs 1M. Can > you describe your test workload and provide before and after traces? > Hi. I update kernel version to 4.0.5. The test information as shown below: The base information: 03:28:13-root@server-186:~$uname -r 4.0.5
My simple systemtap script: probe module("rbd").function("rbd_img_request_create") { printf("offset:%lu length:%lu\n", ulong_arg(2), ulong_arg(3)); }
I use dd to execute the test case: dd if=/dev/zero of=/dev/rbd0 bs=4M count=1 oflag=direct
Case one: Without patch 03:30:23-root@server-186:~$cat /sys/block/rbd0/queue/max_sectors_kb 4096 03:30:35-root@server-186:~$cat /sys/block/rbd0/queue/max_segments 128
The output of systemtap for nornal data: offset:0 length:524288 offset:524288 length:524288 offset:1048576 length:524288 offset:1572864 length:524288 offset:2097152 length:524288 offset:2621440 length:524288 offset:3145728 length:524288 offset:3670016 length:524288
Case two:With patch cat /sys/block/rbd0/queue/max_sectors_kb 4096 03:49:14-root@server-186:linux-4.0.5$cat /sys/block/rbd0/queue/max_segments 1024 The output of systemtap for nornal data: offset:0 length:1048576 offset:1048576 length:1048576 offset:2097152 length:1048576 offset:3145728 length:1048576
According to the test, you are right. Because the blk-mq doesn't use any scheduling policy. 03:52:13-root@server-186:linux-4.0.5$cat /sys/block/rbd0/queue/scheduler none
In previous versions of the kernel 4.0, the rbd use the defualt scheduler:cfq
So, I think that the blk-mq need to do more? > Thanks, > > Ilya >
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