On Mon, Aug 24, 2020 at 01:20:25PM +0800, Jiang Biao wrote:
> From: Jiang Biao <benbjiang@xxxxxxxxxxx>
>
> pci_read_config() could block several ms in kernel space, mainly
> caused by the while loop to call pci_user_read_config_dword().
> Singel pci_user_read_config_dword() loop could consume 130us+,
> | pci_user_read_config_dword() {
> | _raw_spin_lock_irq() {
> ! 136.698 us | native_queued_spin_lock_slowpath();
> ! 137.582 us | }
> | pci_read() {
> | raw_pci_read() {
> | pci_conf1_read() {
> 0.230 us | _raw_spin_lock_irqsave();
> 0.035 us | _raw_spin_unlock_irqrestore();
> 8.476 us | }
> 8.790 us | }
> 9.091 us | }
> ! 147.263 us | }
> and dozens of the loop could consume ms+.
>
> If we execute some lspci commands concurrently, ms+ scheduling
> latency could be detected.
>
> Add scheduling chance in the loop to improve the latency.
Thanks for the patch, this makes a lot of sense.
Shouldn't we do the same in pci_write_config()?
> Reported-by: Bin Lai <robinlai@xxxxxxxxxxx>
> Signed-off-by: Jiang Biao <benbjiang@xxxxxxxxxxx>
> ---
> drivers/pci/pci-sysfs.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 6d78df9..3b9f63d 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -708,6 +708,7 @@ static ssize_t pci_read_config(struct file *filp, struct kobject *kobj,
> data[off - init_off + 3] = (val >> 24) & 0xff;
> off += 4;
> size -= 4;
> + cond_resched();
> }
>
> if (size >= 2) {
> --
> 1.8.3.1
>
