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authorPaolo Valente <paolo.valente@linaro.org>2018-03-26 16:06:24 +0200
committerJens Axboe <axboe@kernel.dk>2018-03-26 10:18:27 -0600
commitbc56e2cafa3f80954a278d74bd18349ac3cb8fa5 (patch)
treebf66485253e3055c244b2475c063e66b90657bc3 /block/bfq-iosched.h
parentd558fb51ad3dc7d5f1287d55d0f2e0646af36253 (diff)
block, bfq: lower-bound the estimated peak rate to 1
If a storage device handled by BFQ happens to be slower than 7.5 KB/s for a certain amount of time (in the order of a second), then the estimated peak rate of the device, maintained in BFQ, becomes equal to 0. The reason is the limited precision with which the rate is represented (details on the range of representable values in the comments introduced by this commit). This leads to a division-by-zero error where the estimated peak rate is used as divisor. Such a type of failure has been reported in [1]. This commit addresses this issue by: 1. Lower-bounding the estimated peak rate to 1 2. Adding and improving comments on the range of rates representable [1] https://www.spinics.net/lists/kernel/msg2739205.html Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Paolo Valente <paolo.valente@linaro.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-iosched.h')
-rw-r--r--block/bfq-iosched.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 350c39ae2896..ae2f3dadec44 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -499,7 +499,7 @@ struct bfq_data {
u64 delta_from_first;
/*
* Current estimate of the device peak rate, measured in
- * [BFQ_RATE_SHIFT * sectors/usec]. The left-shift by
+ * [(sectors/usec) / 2^BFQ_RATE_SHIFT]. The left-shift by
* BFQ_RATE_SHIFT is performed to increase precision in
* fixed-point calculations.
*/