| Message ID | 20190515164814.258898-2-dianders@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | spi: A better solution for cros_ec_spi reliability | expand |
On Wed, May 15, 2019 at 9:48 AM Douglas Anderson <dianders@chromium.org> wrote: > > In commit 37a186225a0c ("platform/chrome: cros_ec_spi: Transfer > messages at high priority") we moved transfers to a high priority > workqueue. This helped make them much more reliable. > > ...but, we still saw failures. > > We were actually finding ourselves competing for time with dm-crypt > which also scheduled work on HIGHPRI workqueues. While we can > consider reverting the change that made dm-crypt run its work at > HIGHPRI, the argument in commit a1b89132dc4f ("dm crypt: use > WQ_HIGHPRI for the IO and crypt workqueues") is somewhat compelling. > It does make sense for IO to be scheduled at a priority that's higher > than the default user priority. It also turns out that dm-crypt isn't > alone in using high priority like this. loop_prepare_queue() does > something similar for loopback devices. > > Looking in more detail, it can be seen that the high priority > workqueue isn't actually that high of a priority. It runs at MIN_NICE > which is _fairly_ high priority but still below all real time > priority. > > Should we move cros_ec_spi to real time priority to fix our problems, > or is this just escalating a priority war? I'll argue here that > cros_ec_spi _does_ belong at real time priority. Specifically > cros_ec_spi actually needs to run quickly for correctness. As I > understand this is exactly what real time priority is for. > > There currently doesn't appear to be any way to use the standard > workqueue APIs with a real time priority, so we'll switch over to > using using a kthread worker. We'll match the priority that the SPI > core uses when it wants to do things on a realtime thread and just use > "MAX_RT_PRIO - 1". > > This commit plus the patch ("platform/chrome: cros_ec_spi: Request the > SPI thread be realtime") are enough to get communications very close > to 100% reliable (the only known problem left is when serial console > is turned on, which isn't something that happens in shipping devices). > Specifically this test case now passes (tested on rk3288-veyron-jerry): > > dd if=/dev/zero of=/var/log/foo.txt bs=4M count=512& > while true; do > ectool version > /dev/null; > done > > It should be noted that "/var/log" is encrypted (and goes through > dm-crypt) and also passes through a loopback device. > > Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Guenter Roeck <groeck@chromium.org>
Hi, On 15/5/19 19:02, Guenter Roeck wrote: > On Wed, May 15, 2019 at 9:48 AM Douglas Anderson <dianders@chromium.org> wrote: >> >> In commit 37a186225a0c ("platform/chrome: cros_ec_spi: Transfer >> messages at high priority") we moved transfers to a high priority >> workqueue. This helped make them much more reliable. >> >> ...but, we still saw failures. >> >> We were actually finding ourselves competing for time with dm-crypt >> which also scheduled work on HIGHPRI workqueues. While we can >> consider reverting the change that made dm-crypt run its work at >> HIGHPRI, the argument in commit a1b89132dc4f ("dm crypt: use >> WQ_HIGHPRI for the IO and crypt workqueues") is somewhat compelling. >> It does make sense for IO to be scheduled at a priority that's higher >> than the default user priority. It also turns out that dm-crypt isn't >> alone in using high priority like this. loop_prepare_queue() does >> something similar for loopback devices. >> >> Looking in more detail, it can be seen that the high priority >> workqueue isn't actually that high of a priority. It runs at MIN_NICE >> which is _fairly_ high priority but still below all real time >> priority. >> >> Should we move cros_ec_spi to real time priority to fix our problems, >> or is this just escalating a priority war? I'll argue here that >> cros_ec_spi _does_ belong at real time priority. Specifically >> cros_ec_spi actually needs to run quickly for correctness. As I >> understand this is exactly what real time priority is for. >> >> There currently doesn't appear to be any way to use the standard >> workqueue APIs with a real time priority, so we'll switch over to >> using using a kthread worker. We'll match the priority that the SPI >> core uses when it wants to do things on a realtime thread and just use >> "MAX_RT_PRIO - 1". >> >> This commit plus the patch ("platform/chrome: cros_ec_spi: Request the >> SPI thread be realtime") are enough to get communications very close >> to 100% reliable (the only known problem left is when serial console >> is turned on, which isn't something that happens in shipping devices). >> Specifically this test case now passes (tested on rk3288-veyron-jerry): >> >> dd if=/dev/zero of=/var/log/foo.txt bs=4M count=512& >> while true; do >> ectool version > /dev/null; >> done >> >> It should be noted that "/var/log" is encrypted (and goes through >> dm-crypt) and also passes through a loopback device. >> >> Signed-off-by: Douglas Anderson <dianders@chromium.org> > > Reviewed-by: Guenter Roeck <groeck@chromium.org> > Added to the for-next branch for the autobuilders to play with, if all goes well will be queued in chrome-platform-5.3 Thanks, Enric
diff --git a/drivers/platform/chrome/cros_ec_spi.c b/drivers/platform/chrome/cros_ec_spi.c index 8e9451720e73..1e38a885c539 100644 --- a/drivers/platform/chrome/cros_ec_spi.c +++ b/drivers/platform/chrome/cros_ec_spi.c @@ -12,7 +12,7 @@ #include <linux/platform_device.h> #include <linux/slab.h> #include <linux/spi/spi.h> - +#include <uapi/linux/sched/types.h> /* The header byte, which follows the preamble */ #define EC_MSG_HEADER 0xec @@ -67,12 +67,14 @@ * is sent when we want to turn on CS at the start of a transaction. * @end_of_msg_delay: used to set the delay_usecs on the spi_transfer that * is sent when we want to turn off CS at the end of a transaction. + * @high_pri_worker: Used to schedule high priority work. */ struct cros_ec_spi { struct spi_device *spi; s64 last_transfer_ns; unsigned int start_of_msg_delay; unsigned int end_of_msg_delay; + struct kthread_worker *high_pri_worker; }; typedef int (*cros_ec_xfer_fn_t) (struct cros_ec_device *ec_dev, @@ -89,7 +91,7 @@ typedef int (*cros_ec_xfer_fn_t) (struct cros_ec_device *ec_dev, */ struct cros_ec_xfer_work_params { - struct work_struct work; + struct kthread_work work; cros_ec_xfer_fn_t fn; struct cros_ec_device *ec_dev; struct cros_ec_command *ec_msg; @@ -632,7 +634,7 @@ static int do_cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev, return ret; } -static void cros_ec_xfer_high_pri_work(struct work_struct *work) +static void cros_ec_xfer_high_pri_work(struct kthread_work *work) { struct cros_ec_xfer_work_params *params; @@ -644,12 +646,14 @@ static int cros_ec_xfer_high_pri(struct cros_ec_device *ec_dev, struct cros_ec_command *ec_msg, cros_ec_xfer_fn_t fn) { - struct cros_ec_xfer_work_params params; - - INIT_WORK_ONSTACK(¶ms.work, cros_ec_xfer_high_pri_work); - params.ec_dev = ec_dev; - params.ec_msg = ec_msg; - params.fn = fn; + struct cros_ec_spi *ec_spi = ec_dev->priv; + struct cros_ec_xfer_work_params params = { + .work = KTHREAD_WORK_INIT(params.work, + cros_ec_xfer_high_pri_work), + .ec_dev = ec_dev, + .ec_msg = ec_msg, + .fn = fn, + }; /* * This looks a bit ridiculous. Why do the work on a @@ -660,9 +664,8 @@ static int cros_ec_xfer_high_pri(struct cros_ec_device *ec_dev, * context switched out for too long and the EC giving up on * the transfer. */ - queue_work(system_highpri_wq, ¶ms.work); - flush_work(¶ms.work); - destroy_work_on_stack(¶ms.work); + kthread_queue_work(ec_spi->high_pri_worker, ¶ms.work); + kthread_flush_work(¶ms.work); return params.ret; } @@ -694,6 +697,40 @@ static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev) ec_spi->end_of_msg_delay = val; } +static void cros_ec_spi_high_pri_release(void *worker) +{ + kthread_destroy_worker(worker); +} + +static int cros_ec_spi_devm_high_pri_alloc(struct device *dev, + struct cros_ec_spi *ec_spi) +{ + struct sched_param sched_priority = { + .sched_priority = MAX_RT_PRIO - 1, + }; + int err; + + ec_spi->high_pri_worker = + kthread_create_worker(0, "cros_ec_spi_high_pri"); + + if (IS_ERR(ec_spi->high_pri_worker)) { + err = PTR_ERR(ec_spi->high_pri_worker); + dev_err(dev, "Can't create cros_ec high pri worker: %d\n", err); + return err; + } + + err = devm_add_action_or_reset(dev, cros_ec_spi_high_pri_release, + ec_spi->high_pri_worker); + if (err) + return err; + + err = sched_setscheduler_nocheck(ec_spi->high_pri_worker->task, + SCHED_FIFO, &sched_priority); + if (err) + dev_err(dev, "Can't set cros_ec high pri priority: %d\n", err); + return err; +} + static int cros_ec_spi_probe(struct spi_device *spi) { struct device *dev = &spi->dev; @@ -732,6 +769,10 @@ static int cros_ec_spi_probe(struct spi_device *spi) ec_spi->last_transfer_ns = ktime_get_ns(); + err = cros_ec_spi_devm_high_pri_alloc(dev, ec_spi); + if (err) + return err; + err = cros_ec_register(ec_dev); if (err) { dev_err(dev, "cannot register EC\n");
In commit 37a186225a0c ("platform/chrome: cros_ec_spi: Transfer messages at high priority") we moved transfers to a high priority workqueue. This helped make them much more reliable. ...but, we still saw failures. We were actually finding ourselves competing for time with dm-crypt which also scheduled work on HIGHPRI workqueues. While we can consider reverting the change that made dm-crypt run its work at HIGHPRI, the argument in commit a1b89132dc4f ("dm crypt: use WQ_HIGHPRI for the IO and crypt workqueues") is somewhat compelling. It does make sense for IO to be scheduled at a priority that's higher than the default user priority. It also turns out that dm-crypt isn't alone in using high priority like this. loop_prepare_queue() does something similar for loopback devices. Looking in more detail, it can be seen that the high priority workqueue isn't actually that high of a priority. It runs at MIN_NICE which is _fairly_ high priority but still below all real time priority. Should we move cros_ec_spi to real time priority to fix our problems, or is this just escalating a priority war? I'll argue here that cros_ec_spi _does_ belong at real time priority. Specifically cros_ec_spi actually needs to run quickly for correctness. As I understand this is exactly what real time priority is for. There currently doesn't appear to be any way to use the standard workqueue APIs with a real time priority, so we'll switch over to using using a kthread worker. We'll match the priority that the SPI core uses when it wants to do things on a realtime thread and just use "MAX_RT_PRIO - 1". This commit plus the patch ("platform/chrome: cros_ec_spi: Request the SPI thread be realtime") are enough to get communications very close to 100% reliable (the only known problem left is when serial console is turned on, which isn't something that happens in shipping devices). Specifically this test case now passes (tested on rk3288-veyron-jerry): dd if=/dev/zero of=/var/log/foo.txt bs=4M count=512& while true; do ectool version > /dev/null; done It should be noted that "/var/log" is encrypted (and goes through dm-crypt) and also passes through a loopback device. Signed-off-by: Douglas Anderson <dianders@chromium.org> --- Changes in v4: - No needless init of err in cros_ec_spi_devm_high_pri_alloc (Guenter). - Removed blank lines near #includes (Guenter). - Switch to kthread_create_worker() and fix error handling (Guenter). - Cleaner devm code (Guenter). Changes in v3: - cros_ec realtime patch replaces revert; now patch #1 Changes in v2: None drivers/platform/chrome/cros_ec_spi.c | 65 ++++++++++++++++++++++----- 1 file changed, 53 insertions(+), 12 deletions(-)