Messages in this thread Patch in this message | | | Subject | Re: [PATCH 0/3] fix interrupt swamp in NVMe | From | John Garry <> | Date | Tue, 20 Aug 2019 09:59:32 +0100 |
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On 20/08/2019 09:25, Ming Lei wrote: > On Tue, Aug 20, 2019 at 2:14 PM <longli@linuxonhyperv.com> wrote: >> >> From: Long Li <longli@microsoft.com> >> >> This patch set tries to fix interrupt swamp in NVMe devices. >> >> On large systems with many CPUs, a number of CPUs may share one NVMe hardware >> queue. It may have this situation where several CPUs are issuing I/Os, and >> all the I/Os are returned on the CPU where the hardware queue is bound to. >> This may result in that CPU swamped by interrupts and stay in interrupt mode >> for extended time while other CPUs continue to issue I/O. This can trigger >> Watchdog and RCU timeout, and make the system unresponsive. >> >> This patch set addresses this by enforcing scheduling and throttling I/O when >> CPU is starved in this situation. >> >> Long Li (3): >> sched: define a function to report the number of context switches on a >> CPU >> sched: export idle_cpu() >> nvme: complete request in work queue on CPU with flooded interrupts >> >> drivers/nvme/host/core.c | 57 +++++++++++++++++++++++++++++++++++++++- >> drivers/nvme/host/nvme.h | 1 + >> include/linux/sched.h | 2 ++ >> kernel/sched/core.c | 7 +++++ >> 4 files changed, 66 insertions(+), 1 deletion(-) > > Another simpler solution may be to complete request in threaded interrupt > handler for this case. Meantime allow scheduler to run the interrupt thread > handler on CPUs specified by the irq affinity mask, which was discussed by > the following link: > > https://lore.kernel.org/lkml/e0e9478e-62a5-ca24-3b12-58f7d056383e@huawei.com/ > > Could you try the above solution and see if the lockup can be avoided? > John Garry > should have workable patch.
Yeah, so we experimented with changing the interrupt handling in the SCSI driver I maintain to use a threaded handler IRQ handler plus patch below, and saw a significant throughput boost:
--->8
Subject: [PATCH] genirq: Add support to allow thread to use hard irq affinity
Currently the cpu allowed mask for the threaded part of a threaded irq handler will be set to the effective affinity of the hard irq.
Typically the effective affinity of the hard irq will be for a single cpu. As such, the threaded handler would always run on the same cpu as the hard irq.
We have seen scenarios in high data-rate throughput testing that the cpu handling the interrupt can be totally saturated handling both the hard interrupt and threaded handler parts, limiting throughput.
Add IRQF_IRQ_AFFINITY flag to allow the driver requesting the threaded interrupt to decide on the policy of which cpu the threaded handler may run.
Signed-off-by: John Garry <john.garry@huawei.com>
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 5b8328a99b2a..48e8b955989a 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -61,6 +61,9 @@ * interrupt handler after suspending interrupts. For system * wakeup devices users need to implement wakeup detection in * their interrupt handlers. + * IRQF_IRQ_AFFINITY - Use the hard interrupt affinity for setting the cpu + * allowed mask for the threaded handler of a threaded interrupt + * handler, rather than the effective hard irq affinity. */ #define IRQF_SHARED 0x00000080 #define IRQF_PROBE_SHARED 0x00000100 @@ -74,6 +77,7 @@ #define IRQF_NO_THREAD 0x00010000 #define IRQF_EARLY_RESUME 0x00020000 #define IRQF_COND_SUSPEND 0x00040000 +#define IRQF_IRQ_AFFINITY 0x00080000
#define IRQF_TIMER (__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c index e8f7f179bf77..cb483a055512 100644 --- a/kernel/irq/manage.c +++ b/kernel/irq/manage.c @@ -966,9 +966,13 @@ irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action) * mask pointer. For CPU_MASK_OFFSTACK=n this is optimized out. */ if (cpumask_available(desc->irq_common_data.affinity)) { + struct irq_data *irq_data = &desc->irq_data; const struct cpumask *m;
- m = irq_data_get_effective_affinity_mask(&desc->irq_data); + if (action->flags & IRQF_IRQ_AFFINITY) + m = desc->irq_common_data.affinity; + else + m = irq_data_get_effective_affinity_mask(irq_data); cpumask_copy(mask, m); } else { valid = false; -- 2.17.1 As Ming mentioned in that same thread, we could even make this policy for managed interrupts.
Cheers, John
> > Thanks, > Ming Lei > > . >
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