Re: accessing a PCIe register from userspace through kmem or other ways ?

From: Konstantin Belousov <kostikbel_at_gmail.com>
Date: Tue, 5 Apr 2016 09:10:13 +0300
On Mon, Apr 04, 2016 at 09:02:49PM -0700, John Baldwin wrote:
> kib_at_ fixed /dev/mem to handle addresses beyond the direct map limit to use
> temporary mappings instead of failing with EFAULT in 277051 which was only
> committed to HEAD last January, so well after 8.2.

The mmap(2) interface to /dev/mem did not have the issue ever.  The problem
was only with the read(2)/write(2) accesses.

>From what I understand, since the goal of the OP was to measure BAR
access latencies, read(2) (or write) is unsuitable for him for obvious
reasons.
Received on Tue Apr 05 2016 - 04:10:18 UTC

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