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SubjectRe: [PATCH 3/3] x86: UV2 BAU hang workarounds

* Cliff Wickman <cpw@sgi.com> wrote:

> On SGI's UV2 the BAU (Broadcast Assist Unit) driver can hang under a
> heavy load. To cure this:
>
> - Disable the UV2 extended status mode (see UV2_EXT_SHFT), as this
> mode changes BAU behavior in more ways then just delivering an extra bit
> of status. Revert status to just two meaningful bits, like UV1.
> - Use no IPI-style resets on UV2. Just give up the request for whatever the
> reason it failed and let it be accomplished with the legacy IPI method.
> - Use no alternate sending descriptor (the former UV2 workaround
> bcp->using_desc and handle_uv2_busy() stuff). Just disable the use of the
> BAU for a period of time in favor of the legacy IPI method when the h/w bug
> leaves a descriptor busy.
> -- new tunable: giveup_limit determines the threshold at which a hub is
> so plugged that it should do all requests with the legacy IPI method for a
> period of time
> -- generalize disable_for_congestion() (renamed disable_for_period()) for
> use whenever a hub should avoid using the BAU for a period of time
>
> Misc:
> - fix find_another_by_swack(), which is part of the UV2 bug workaround
> - correct and clarify the statistics (new stats s_overipilimit s_giveuplimit
> s_enters s_ipifordisabled s_plugged s_congested)

Sigh, it looks like something that ought to be 7 successive,
easy to review commits got mixed up into a single, huge, hard to
review commit. How did that happen?

Thanks,

Ingo


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