2015-07-23 21:55:33

by Spencer Baugh

Subject: [PATCH] aer: add cond_resched to aer_isr

From: Joern Engel <[email protected]>

Multiple nested loops. I have observed 590ms scheduler latency caused
by this loop and interrupts. Interrupts were responsible for 190ms, the
rest could have been avoided with a cond_resched.

Signed-off-by: Joern Engel <[email protected]>
Signed-off-by: Spencer Baugh <[email protected]>
---
drivers/pci/pcie/aer/aerdrv_core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
index 9803e3d..32b1b5c 100644
--- a/drivers/pci/pcie/aer/aerdrv_core.c
+++ b/drivers/pci/pcie/aer/aerdrv_core.c
@@ -780,8 +780,10 @@ void aer_isr(struct work_struct *work)
struct aer_err_source uninitialized_var(e_src);

mutex_lock(&rpc->rpc_mutex);
- while (get_e_source(rpc, &e_src))
+ while (get_e_source(rpc, &e_src)) {
aer_isr_one_error(p_device, &e_src);
+ cond_resched();
+ }
mutex_unlock(&rpc->rpc_mutex);

wake_up(&rpc->wait_release);
--
2.5.0.rc3

2015-08-03 22:44:26

by Bjorn Helgaas

Subject: Re: [PATCH] aer: add cond_resched to aer_isr

Hi Spencer & Joern,

On Thu, Jul 23, 2015 at 02:54:32PM -0700, Spencer Baugh wrote:
> From: Joern Engel <[email protected]>
>
> Multiple nested loops. I have observed 590ms scheduler latency caused
> by this loop and interrupts. Interrupts were responsible for 190ms, the
> rest could have been avoided with a cond_resched.

I'm not disagreeing with this patch, but it would be helpful to sketch
the outline of the "multiple nested loop" problem here. This might be
a hint that we could do even better by rethinking the algorithm reduce
the nesting.

> Signed-off-by: Joern Engel <[email protected]>
> Signed-off-by: Spencer Baugh <[email protected]>
> ---
> drivers/pci/pcie/aer/aerdrv_core.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pcie/aer/aerdrv_core.c b/drivers/pci/pcie/aer/aerdrv_core.c
> index 9803e3d..32b1b5c 100644
> --- a/drivers/pci/pcie/aer/aerdrv_core.c
> +++ b/drivers/pci/pcie/aer/aerdrv_core.c
> @@ -780,8 +780,10 @@ void aer_isr(struct work_struct *work)
> struct aer_err_source uninitialized_var(e_src);
>
> mutex_lock(&rpc->rpc_mutex);
> - while (get_e_source(rpc, &e_src))
> + while (get_e_source(rpc, &e_src)) {
> aer_isr_one_error(p_device, &e_src);
> + cond_resched();
> + }
> mutex_unlock(&rpc->rpc_mutex);
>
> wake_up(&rpc->wait_release);
> --
> 2.5.0.rc3
>