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
Also:
- 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)
Signed-off-by: Cliff Wickman <cpw@sgi.com>
Link: http://lkml.kernel.org/r/20120622131459.GC31884@sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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