From: Jiang Biao <benbjiang@gmail.com>
To: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>,
Jiang Biao <benbjiang@tencent.com>,
Bin Lai <robinlai@tencent.com>
Subject: Re: [PATCH] driver/pci: reduce the single block time in pci_read_config
Date: Thu, 27 Aug 2020 17:49:12 +0800 [thread overview]
Message-ID: <CAPJCdBmLeD84kRXWmuPj+-_2kBLmZ8wR-uJ641xShza6E52D0w@mail.gmail.com> (raw)
In-Reply-To: <20200824052025.48362-1-benbjiang@tencent.com>
kindly ping :)
On Mon, 24 Aug 2020 at 13:20, Jiang Biao <benbjiang@gmail.com> wrote:
>
> From: Jiang Biao <benbjiang@tencent.com>
>
> 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.
>
> Reported-by: Bin Lai <robinlai@tencent.com>
> Signed-off-by: Jiang Biao <benbjiang@tencent.com>
> ---
> 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
>
next prev parent reply other threads:[~2020-08-27 9:49 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-24 5:20 [PATCH] driver/pci: reduce the single block time in pci_read_config Jiang Biao
2020-08-27 9:49 ` Jiang Biao [this message]
2020-09-10 1:25 ` Bjorn Helgaas
2020-09-10 1:54 ` Jiang Biao
2020-09-10 1:59 ` Bjorn Helgaas
2020-09-10 2:18 ` Jiang Biao
2020-09-13 4:27 ` Jiang Biao
2020-09-16 16:56 ` Bjorn Helgaas
2020-09-17 0:22 ` Jiang Biao
2020-09-17 17:32 ` Bjorn Helgaas
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