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
