Re: [PATCH] mtd: revert "spi-nor: intel: provide a range for poll_timout"

Alexander Sverdlin
2020-07-22T16:37:31Z

Hello Luis,

thank you for the patch!

On 11/06/2020 00:46, Luis Alberto Herrera wrote:
> This change reverts aba3a882a178: "mtd: spi-nor: intel: provide a range
> for poll_timout". That change introduces a performance regression when
> reading sequentially from flash. Logging calls to intel_spi_read without
> this change we get:
>
> Start MTD read
> [ 20.045527] intel_spi_read(from=1800000, len=400000)
> [ 20.045527] intel_spi_read(from=1800000, len=400000)
> [ 282.199274] intel_spi_read(from=1c00000, len=400000)
> [ 282.199274] intel_spi_read(from=1c00000, len=400000)
> [ 544.351528] intel_spi_read(from=2000000, len=400000)
> [ 544.351528] intel_spi_read(from=2000000, len=400000)
> End MTD read
>
> With this change:
>
> Start MTD read
> [ 21.942922] intel_spi_read(from=1c00000, len=400000)
> [ 21.942922] intel_spi_read(from=1c00000, len=400000)
> [ 23.784058] intel_spi_read(from=2000000, len=400000)
> [ 23.784058] intel_spi_read(from=2000000, len=400000)
> [ 25.625006] intel_spi_read(from=2400000, len=400000)
> [ 25.625006] intel_spi_read(from=2400000, len=400000)
> End MTD read

I've performed my testing as well and got the following results:

Vanilla Linux 4.9 (i.e. before the introduction of the offending
patch):

dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
1280+0 records in
1280+0 records out
5242880 bytes (5.2 MB, 5.0 MiB) copied, 3.91981 s, 1.3 MB/s

Vanilla 4.19 (i.e. with offending patch):

dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
1280+0 records in
1280+0 records out
5242880 bytes (5.2 MB, 5.0 MiB) copied, 6.70891 s, 781 kB/s

4.19 + revert:

dd if=/dev/flash/by-name/XXX of=/dev/null bs=4k
1280+0 records in
1280+0 records out
5242880 bytes (5.2 MB, 5.0 MiB) copied, 3.90503 s, 1.3 MB/s

Therefore it looks good from my PoV:

Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>

> Signed-off-by: Luis Alberto Herrera <luisalberto@google.com>
> Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
> drivers/mtd/spi-nor/controllers/intel-spi.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mtd/spi-nor/controllers/intel-spi.c b/drivers/mtd/spi-nor/controllers/intel-spi.c
> index 61d2a0ad2131..2b89361a0d3a 100644
> --- a/drivers/mtd/spi-nor/controllers/intel-spi.c
> +++ b/drivers/mtd/spi-nor/controllers/intel-spi.c
> @@ -292,7 +292,7 @@ static int intel_spi_wait_hw_busy(struct intel_spi *ispi)
> u32 val;
>
> return readl_poll_timeout(ispi->base + HSFSTS_CTL, val,
> - !(val & HSFSTS_CTL_SCIP), 40,
> + !(val & HSFSTS_CTL_SCIP), 0,
> INTEL_SPI_TIMEOUT * 1000);
> }
>
> @@ -301,7 +301,7 @@ static int intel_spi_wait_sw_busy(struct intel_spi *ispi)
> u32 val;
>
> return readl_poll_timeout(ispi->sregs + SSFSTS_CTL, val,
> - !(val & SSFSTS_CTL_SCIP), 40,
> + !(val & SSFSTS_CTL_SCIP), 0,
> INTEL_SPI_TIMEOUT * 1000);
> }
>
>

--
Best regards,
Alexander Sverdlin.