> +/* update queue busy with EWMA (7/8 * ewma(t) + 1/8 * busy(t + 1)) */ > +static void blk_mq_update_hctx_busy(struct blk_mq_hw_ctx *hctx, unsigned int busy) Overly long line. Also busy really is a bool, so I think we should pass it as such. Also I think this needs a much better comment describing why we are using this algorith. Also expanding the EWMA acronym would help, I had to look it up first. > + const unsigned weight = 8; > + const unsigned factor = 4; Where do these magic constants come from? > + unsigned int ewma; > + > + if (hctx->queue->elevator) > + return; > + > + ewma = READ_ONCE(hctx->busy); > + > + ewma *= weight - 1; > + ewma += busy << factor; With the bool parameter and expanding the "factor" which really is a shift value this would be: if (busy) ewma += 16; which at least is a little more understandable, although still not great.
