From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: [PATCH 1.5/2 v2] dm stripe: optimize sector division Date: Wed, 28 Jul 2010 11:21:04 -0400 Message-ID: <20100728152104.GA5607@redhat.com> References: <20100728135332.GA31387@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Mikulas Patocka Cc: dm-devel@redhat.com, Alasdair G Kergon List-Id: dm-devel.ids From: Mikulas Patocka Optimize sector division --- if the number of stripes is a power of two, we don't have to do expensive division and can do shift and mask instead. Signed-off-by: Mikulas Patocka Signed-off-by: Mike Snitzer --- drivers/md/dm-stripe.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) v2: minor code cleanup in stripe_map_sector Index: linux-2.6-block/drivers/md/dm-stripe.c =================================================================== --- linux-2.6-block.orig/drivers/md/dm-stripe.c +++ linux-2.6-block/drivers/md/dm-stripe.c @@ -25,6 +25,7 @@ struct stripe { struct stripe_c { uint32_t stripes; + int stripes_shift; /* The size of this target / num. stripes */ sector_t stripe_width; @@ -164,6 +165,10 @@ static int stripe_ctr(struct dm_target * sc->ti = ti; sc->stripes = stripes; + if (!(stripes & (stripes - 1))) + sc->stripes_shift = ffs(stripes) - 1; + else + sc->stripes_shift = -1; sc->stripe_width = width; ti->split_io = chunk_size; ti->num_flush_requests = stripes; @@ -213,7 +218,12 @@ static void stripe_map_sector(struct str { sector_t offset = sector - sc->ti->begin; sector_t chunk = offset >> sc->chunk_shift; - *stripe = sector_div(chunk, sc->stripes); + + if (likely(sc->stripes_shift >= 0)) { + *stripe = chunk & ((1 << sc->stripes_shift) - 1); + chunk >>= sc->stripes_shift; + } else + *stripe = sector_div(chunk, sc->stripes); *result = (chunk << sc->chunk_shift) | (offset & sc->chunk_mask); }