Hi Arnd,

On Thu, May 20, 2021 at 3:15 PM Arnd Bergmann [off-list ref] wrote:

On Thu, May 20, 2021 at 9:43 AM Geert Uytterhoeven [off-list ref] wrote:

quoted

On Tue, 18 May 2021, David Sterba wrote:

quoted

--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c

@@ -1988,6 +1993,60 @@ static void scrub_page_put(struct scrub_page *spage)
      }

}

+/*
+ * Throttling of IO submission, bandwidth-limit based, the timeslice is 1
+ * second.  Limit can be set via /sys/fs/UUID/devinfo/devid/scrub_speed_max.
+ */
+static void scrub_throttle(struct scrub_ctx *sctx)
+{
+     const int time_slice = 1000;
+     struct scrub_bio *sbio;
+     struct btrfs_device *device;
+     s64 delta;
+     ktime_t now;
+     u32 div;
+     u64 bwlimit;
+
+     sbio = sctx->bios[sctx->curr];
+     device = sbio->dev;
+     bwlimit = READ_ONCE(device->scrub_speed_max);
+     if (bwlimit == 0)
+             return;
+
+     /*
+      * Slice is divided into intervals when the IO is submitted, adjust by
+      * bwlimit and maximum of 64 intervals.
+      */
+     div = max_t(u32, 1, (u32)(bwlimit / (16 * 1024 * 1024)));
+     div = min_t(u32, 64, div);
+
+     /* Start new epoch, set deadline */
+     now = ktime_get();
+     if (sctx->throttle_deadline == 0) {
+             sctx->throttle_deadline = ktime_add_ms(now, time_slice / div);

ERROR: modpost: "__udivdi3" [fs/btrfs/btrfs.ko] undefined!

div_u64(bwlimit, div)

If 'time_slice' is in nanoseconds, the best interface to use
is ktime_divns().

Actually this one is not a problem...

quoted

quoted

+             sctx->throttle_sent = 0;
+     }
+
+     /* Still in the time to send? */
+     if (ktime_before(now, sctx->throttle_deadline)) {
+             /* If current bio is within the limit, send it */
+             sctx->throttle_sent += sbio->bio->bi_iter.bi_size;
+             if (sctx->throttle_sent <= bwlimit / div)
+                     return;

Doesn't this also need to be changed?

... but this is.

Sorry. I added the annotation to the wrong line, after devising which
code caused the issue from looking at the generated assembly ;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds