6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Stefan Wahren <wahrenst@xxxxxxx>
[ 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>
---
drivers/char/hw_random/bcm2835-rng.c | 2 +-
drivers/char/hw_random/core.c | 6 ++++++
include/linux/hw_random.h | 1 +
3 files changed, 8 insertions(+), 1 deletion(-)
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 cc002b0c2f0c3..8f31f9d810305 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -680,6 +680,12 @@ 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 77c2885c4c130..2505d58bd5829 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_ */
--
2.42.0
