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

[david mosberger <dmosberger@gmail.com>]

On 9/2/05, Grant Grundler <iod00d@hp.com> wrote:
> 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".

I do not think the basic inX/outX and readX/writeX operations should
involve spinlocks.  That would be really nasty if an MCA/INIT handler
had to call them, for example...

> > 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/

Reads are slow, sure, but writes are not (or should not).

  --david
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