Re: [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 12/06/2020 07:06, Hannes Reinecke wrote:

+out:
+    sbitmap_free(&shared_sb);
+    return res;
+}
+
  static int hctx_tags_bitmap_show(void *data, struct seq_file *m)
  {
      struct blk_mq_hw_ctx *hctx = data;
@@ -823,6 +884,7 @@ static const struct blk_mq_debugfs_attr blk_mq_debugfs_hctx_shared_sbitmap_attrs
      {"busy", 0400, hctx_busy_show},
      {"ctx_map", 0400, hctx_ctx_map_show},
      {"tags", 0400, hctx_tags_show},
+    {"tags_bitmap", 0400, hctx_tags_shared_sbitmap_bitmap_show},
      {"sched_tags", 0400, hctx_sched_tags_show},
      {"sched_tags_bitmap", 0400, hctx_sched_tags_bitmap_show},
      {"io_poll", 0600, hctx_io_poll_show, hctx_io_poll_write},

Ah, right. Here it is.

But I don't get it; why do we have to allocate a temporary bitmap and can't walk the existing shared sbitmap?


Just coming back to this now...

For the bitmap dump - sbitmap_bitmap_show() - it is passed a struct sbitmap *. So we have to filter into a temp per-hctx struct sbitmap. We could change sbitmap_bitmap_show() to accept a filter iterator - which I think you're getting at - but I am not sure it's worth the change. Or else use the allocated sbitmap for the hctx, as above*, but I may be remove that (see 4/12 response).

Yes, I do think I would prefer updating sbitmap_bitmap_show() to accept a filter. Especially as Ming Lei has now updated the tag iterators to accept a filter, too, so it should be an easy change.

Can you please explain how you would use an iterator here?

In fact, I am half thinking of dropping this patch entirely.

So I feel that current behavior is a little strange, as some may expect /sys/kernel/debug/block/sdX/hctxY/tags_bitmap would only show tags for hctxY for sdX, while it is for hctxY for all queues. Same for /sys/kernel/debug/block/sdX/hctxY/tags

And then, for what we have in this patch:

static void hctx_filter_sb(struct sbitmap *sb, struct blk_mq_hw_ctx *hctx)
{
struct hctx_sb_data hctx_sb_data = { .sb = sb, .hctx = hctx };

blk_mq_queue_tag_busy_iter(hctx->queue, hctx_filter_fn, &hctx_sb_data);
}

This will give tags only for this queue. So not the same. So I feel it's better to change current behavior (so consistent) or change neither. And changing current behavior would also mean we need to change what we show in /sys/kernel/debug/block/sdX/hctxY/tags, and that looks troublesome also.

Opinion?

Thanks,
John



[Index of Archives]     [Linux RAID]     [Linux SCSI]     [Linux ATA RAID]     [IDE]     [Linux Wireless]     [Linux Kernel]     [ATH6KL]     [Linux Bluetooth]     [Linux Netdev]     [Kernel Newbies]     [Security]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Device Mapper]

  Powered by Linux