Hi, On Sun, Jul 26, 2020 at 2:44 AM Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx> wrote: > > Hi Stephen, > > On 7/25/20 12:17 AM, Stephen Boyd wrote: > > From: Stephen Boyd <swboyd@xxxxxxxxxxxx> > > > > The busy loop in rpmh_rsc_send_data() is written with the assumption > > that the udelay will be preempted by the tcs_tx_done() irq handler when > > the TCS slots are all full. This doesn't hold true when the calling > > thread is an irqthread and the tcs_tx_done() irq is also an irqthread. > > That's because kernel irqthreads are SCHED_FIFO and thus need to > > voluntarily give up priority by calling into the scheduler so that other > > threads can run. > > > > I see RCU stalls when I boot with irqthreads on the kernel commandline > > because the modem remoteproc driver is trying to send an rpmh async > > message from an irqthread that needs to give up the CPU for the rpmh > > irqthread to run and clear out tcs slots. > > > > rcu: INFO: rcu_preempt self-detected stall on CPU > > rcu: 0-....: (1 GPs behind) idle=402/1/0x4000000000000002 softirq=2108/2109 fqs=4920 > > (t=21016 jiffies g=2933 q=590) > > Task dump for CPU 0: > > irq/11-smp2p R running task 0 148 2 0x00000028 > > Call trace: > > dump_backtrace+0x0/0x154 > > show_stack+0x20/0x2c > > sched_show_task+0xfc/0x108 > > dump_cpu_task+0x44/0x50 > > rcu_dump_cpu_stacks+0xa4/0xf8 > > rcu_sched_clock_irq+0x7dc/0xaa8 > > update_process_times+0x30/0x54 > > tick_sched_handle+0x50/0x64 > > tick_sched_timer+0x4c/0x8c > > __hrtimer_run_queues+0x21c/0x36c > > hrtimer_interrupt+0xf0/0x22c > > arch_timer_handler_phys+0x40/0x50 > > handle_percpu_devid_irq+0x114/0x25c > > __handle_domain_irq+0x84/0xc4 > > gic_handle_irq+0xd0/0x178 > > el1_irq+0xbc/0x180 > > save_return_addr+0x18/0x28 > > return_address+0x54/0x88 > > preempt_count_sub+0x40/0x88 > > _raw_spin_unlock_irqrestore+0x4c/0x6c > > ___ratelimit+0xd0/0x128 > > rpmh_rsc_send_data+0x24c/0x378 > > __rpmh_write+0x1b0/0x208 > > rpmh_write_async+0x90/0xbc > > rpmhpd_send_corner+0x60/0x8c > > rpmhpd_aggregate_corner+0x8c/0x124 > > rpmhpd_set_performance_state+0x8c/0xbc > > _genpd_set_performance_state+0xdc/0x1b8 > > dev_pm_genpd_set_performance_state+0xb8/0xf8 > > q6v5_pds_disable+0x34/0x60 [qcom_q6v5_mss] > > qcom_msa_handover+0x38/0x44 [qcom_q6v5_mss] > > q6v5_handover_interrupt+0x24/0x3c [qcom_q6v5] > > handle_nested_irq+0xd0/0x138 > > qcom_smp2p_intr+0x188/0x200 > > irq_thread_fn+0x2c/0x70 > > irq_thread+0xfc/0x14c > > kthread+0x11c/0x12c > > ret_from_fork+0x10/0x18 > > > > This busy loop naturally lends itself to using a wait queue so that each > > thread that tries to send a message will sleep waiting on the waitqueue > > and only be woken up when a free slot is available. This should make > > things more predictable too because the scheduler will be able to sleep > > tasks that are waiting on a free tcs instead of the busy loop we > > currently have today. > > > > Cc: Douglas Anderson <dianders@xxxxxxxxxxxx> > > Cc: Maulik Shah <mkshah@xxxxxxxxxxxxxx> > > Cc: Lina Iyer <ilina@xxxxxxxxxxxxxx> > > Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx> > > --- > > > > Changes in v2: > > * Document tcs_wait > > * Move wake_up() outside of the spinlock > > * Document claim_tcs_for_req() > > > > drivers/soc/qcom/rpmh-internal.h | 4 ++ > > drivers/soc/qcom/rpmh-rsc.c | 115 +++++++++++++++---------------- > > 2 files changed, 58 insertions(+), 61 deletions(-) > > This also fixes an issue related to TCS busy, seen with Venus driver > with these [1] patches applied. > > Tested-by: Stanimir Varbanov <stanimir.varbanov@xxxxxxxxxx> > > -- > regards, > Stan > > [1] https://lkml.org/lkml/2020/7/23/394 It worries me that you say that this fixes any issues for you. Specifically I don't see how this could fix anything except: 1. Fix the problem with irqthreads, which is how Stephen originally found this. 2. Fix things to be a little more efficient. 3. Avoid the small handful of messages that show up during normal usage that look like: TCS Busy, retrying RPMH message send: addr=... I'm guessing you're referring to #3. Is that correct? If so, you might want to double-check to confirm that you aren't totally spamming the RPMh bus with your patch series. I found that when I was seeing a lot of "TCS Busy, retrying RPMH message send" spammed to the console that it was a sign that the code was being really inefficient. Specifically the code to add interconnect bandwidth and OPP to the SPI drivers would run at "runtime_suspend" and "runtime_resume". For our SPI drivers this meant that they were running after every single transfer, and they were quite slow. If your code is doing similar then you probably have a problem. The problem was fixed by adding an autosuspend delay. References (from linuxnext): 8592eb959ad4 spi: spi-qcom-qspi: Set an autosuspend delay of 250 ms cfdab2cd85ec spi: spi-geni-qcom: Set an autosuspend delay of 250 ms Also if your code is adjusting its clock rate too frequently it can now trigger similar problems. References: 2124331411a1 spi: spi-qcom-qspi: Avoid clock setting if not needed 5f219524ec6e spi: spi-geni-qcom: Set the clock properly at runtime resume 68890e20942b spi: spi-geni-qcom: Avoid clock setting if not needed -Doug
