Re: [PATCH 2.6.13] IOCHK interface for I/O error handling/detecting (for ia64)

Grant Grundler
2005-09-02T16:48:28Z

On Thu, Sep 01, 2005 at 05:45:54PM -0500, Brent Casavant wrote:
...
> The first is serialization of all I/O reads and writes. This will
> be a severe problem on systems with large numbers of PCI buses, the
> very type of system that stands the most to gain in reliability from
> these efforts. At a minimum any locking should be done on a per-bus
> basis.

The lock could be per "error domain" - that would require some
arch specific support though to define the scope of the "error domain".

> The second is the raw performance penalty from acquiring and dropping
> a lock with every read and write. This will be a substantial amount
> of activity for any I/O-intensive system, heck even for moderate I/O
> levels.

Sorry - I think this is BS.

Please run mmio_test on your box and share the results.
mmio_test is available here:
svn co http://svn.gnumonks.org/trunk/mmio_test/

Then we can talk about the cost of spinlocks vs cost of MMIO access.

thanks,
grant