diff options
| author | Stefan Wahren <wahrenst@gmx.net> | 2023-09-06 01:27:57 +0200 |
|---|---|---|
| committer | Herbert Xu <herbert@gondor.apana.org.au> | 2023-09-15 18:29:45 +0800 |
| commit | b58a36008bfa1aadf55f516bcbfae40c779eb54b (patch) | |
| tree | f689c99a598d2773bcdbb72c01a5c1a6b85ef070 /drivers/char/hw_random | |
| parent | c977950146720abff14e46d8c53f5638b06a9182 (diff) | |
hwrng: bcm2835 - Fix hwrng throughput regression
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@gmx.net/
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'drivers/char/hw_random')
| -rw-r--r-- | drivers/char/hw_random/bcm2835-rng.c | 2 | ||||
| -rw-r--r-- | drivers/char/hw_random/core.c | 6 |
2 files changed, 7 insertions, 1 deletions
diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c index eb04b12f9f01..b03e80300627 100644 --- a/drivers/char/hw_random/bcm2835-rng.c +++ b/drivers/char/hw_random/bcm2835-rng.c @@ -70,7 +70,7 @@ 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 e3598ec9cfca..420f155d251f 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -678,6 +678,12 @@ 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; |