On Sat, Aug 26, 2023 at 01:28:28PM +0200, Stefan Wahren wrote:
> The recent RCU stall fix caused a massive throughput regression of the
> hwrng on Raspberry Pi 0 - 3. So try to restore a similiar throughput
> as before the RCU stall fix.
>
> Some performance measurements on Raspberry Pi 3B+ (arm64/defconfig):
>
> sudo dd if=/dev/hwrng of=/dev/null count=1 bs=10000
>
> cpu_relax ~138025 Bytes / sec
> hwrng_msleep(1000) ~13 Bytes / sec
> usleep_range(100,200) ~92141 Bytes / sec
>
> Fixes: 96cb9d055445 ("hwrng: bcm2835 - use hwrng_msleep() instead of cpu_relax()")
> Link: https://lore.kernel.org/linux-arm-kernel/bc97ece5-44a3-4c4e-77da-2db3eb66b128@xxxxxxx/
> Signed-off-by: Stefan Wahren <wahrenst@xxxxxxx>
> ---
> drivers/char/hw_random/bcm2835-rng.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
> index e98fcac578d6..3f1b6aaa98ee 100644
> --- a/drivers/char/hw_random/bcm2835-rng.c
> +++ b/drivers/char/hw_random/bcm2835-rng.c
> @@ -14,6 +14,7 @@
> #include <linux/printk.h>
> #include <linux/clk.h>
> #include <linux/reset.h>
> +#include <linux/delay.h>
>
> #define RNG_CTRL 0x0
> #define RNG_STATUS 0x4
> @@ -71,7 +72,7 @@ static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
> while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
> if (!wait)
> return 0;
> - hwrng_msleep(rng, 1000);
> + usleep_range(100, 200);
I think we still need to use the hwrng_msleep function so that the sleep
remains cancelable. Maybe just change the 1000 to 100?
Jason
> }
>
> num_words = rng_readl(priv, RNG_STATUS) >> 24;
> --
> 2.34.1
>
>
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