This is a note to let you know that I've just added the patch titled
hwrng: bcm2835 - Fix hwrng throughput regression
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
hwrng-bcm2835-fix-hwrng-throughput-regression.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 1c1b262764531be69179dfa5ae38d1f909b5e6b2
Author: Stefan Wahren <wahrenst@xxxxxxx>
Date: Wed Sep 6 01:27:57 2023 +0200
hwrng: bcm2835 - Fix hwrng throughput regression
[ Upstream commit b58a36008bfa1aadf55f516bcbfae40c779eb54b ]
The last RCU stall fix caused a massive throughput regression of the
hwrng on Raspberry Pi 0 - 3. hwrng_msleep doesn't sleep precisely enough
and usleep_range doesn't allow scheduling. So try to restore the
best possible throughput by introducing hwrng_yield which interruptable
sleeps for one jiffy.
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
hwrng_yield ~2510 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>
Reviewed-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
index e98fcac578d66..634eab4776f32 100644
--- a/drivers/char/hw_random/bcm2835-rng.c
+++ b/drivers/char/hw_random/bcm2835-rng.c
@@ -71,7 +71,7 @@ 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);
+ hwrng_yield(rng);
}
num_words = rng_readl(priv, RNG_STATUS) >> 24;
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index f34d356fe2c06..599a4bc2c5484 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -679,6 +679,12 @@ long hwrng_msleep(struct hwrng *rng, unsigned int msecs)
}
EXPORT_SYMBOL_GPL(hwrng_msleep);
+long hwrng_yield(struct hwrng *rng)
+{
+ return wait_for_completion_interruptible_timeout(&rng->dying, 1);
+}
+EXPORT_SYMBOL_GPL(hwrng_yield);
+
static int __init hwrng_modinit(void)
{
int ret;
diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h
index 8a3115516a1ba..136e9842120e8 100644
--- a/include/linux/hw_random.h
+++ b/include/linux/hw_random.h
@@ -63,5 +63,6 @@ extern void hwrng_unregister(struct hwrng *rng);
extern void devm_hwrng_unregister(struct device *dve, struct hwrng *rng);
extern long hwrng_msleep(struct hwrng *rng, unsigned int msecs);
+extern long hwrng_yield(struct hwrng *rng);
#endif /* LINUX_HWRANDOM_H_ */
