From: Jiang Biao <benbjiang@tencent.com>
Date: Mon, 24 Aug 2020 05:20:25 +0000 (+0800)
Subject: PCI: Add schedule point in pci_read_config()
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=2ce02a864ac1a2bf99baeb20d38100d2cc413ac2;p=linux.git

PCI: Add schedule point in pci_read_config()

The PCI sysfs "config" file allows large reads, and the resulting PCI
config reads can take several milliseconds to complete.  Testing with the
cyclictest [1] benchmark showed 5ms+ latencies.

Add a schedule point in pci_read_config() to reduce the maximum latency.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-tests.git/

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20200824052025.48362-1-benbjiang@tencent.com
Reported-by: Bin Lai <robinlai@tencent.com>
Signed-off-by: Jiang Biao <benbjiang@tencent.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index 6d78df981d41a..3b9f63d3cad61 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) {