Messages in this thread | | | Subject | Re: [PATCH] mtd: ubi: avoid expensive do_div() on 32-bit machines | From | Zhihao Cheng <> | Date | Wed, 13 Mar 2024 19:29:41 +0800 |
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在 2024/3/13 16:46, Arnd Bergmann 写道: > From: Arnd Bergmann <arnd@arndb.de> > > The use of do_div() in ubi_nvmem_reg_read() makes calling it on > 32-bit machines rather expensive. Since the 'from' variable is > known to be a 32-bit quantity, it is clearly never needed and > can be optimized into a regular division operation. > Do you meet a performance problem on a 32-bit machine? There are too many places invoking do_div, why do you optimize this one? Have you tested the influence on a x86_64 platform after this patch applied? Looks like that do_div is more efficient in x86.
> Fixes: b8a77b9a5f9c ("mtd: ubi: fix NVMEM over UBI volumes on 32-bit systems") > Fixes: 3ce485803da1 ("mtd: ubi: provide NVMEM layer over UBI volumes") > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > --- > drivers/mtd/ubi/nvmem.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/mtd/ubi/nvmem.c b/drivers/mtd/ubi/nvmem.c > index 8aeb9c428e51..a94a1a9aaec1 100644 > --- a/drivers/mtd/ubi/nvmem.c > +++ b/drivers/mtd/ubi/nvmem.c > @@ -6,7 +6,6 @@ > /* UBI NVMEM provider */ > #include "ubi.h" > #include <linux/nvmem-provider.h> > -#include <asm/div64.h> > > /* List of all NVMEM devices */ > static LIST_HEAD(nvmem_devices); > @@ -27,14 +26,15 @@ static int ubi_nvmem_reg_read(void *priv, unsigned int from, > struct ubi_nvmem *unv = priv; > struct ubi_volume_desc *desc; > uint32_t offs; > - uint64_t lnum = from; > + uint32_t lnum; > int err = 0; > > desc = ubi_open_volume(unv->ubi_num, unv->vol_id, UBI_READONLY); > if (IS_ERR(desc)) > return PTR_ERR(desc); > > - offs = do_div(lnum, unv->usable_leb_size); > + offs = from % unv->usable_leb_size; > + lnum = from / unv->usable_leb_size; > while (bytes_left) { > to_read = unv->usable_leb_size - offs; > >
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