linux-kernel - Re: [PATCH 3/3] x86: UV2 BAU hang workarounds

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Message-ID: <20120625100321.GB27081@gmail.com>
Date:	Mon, 25 Jun 2012 12:03:21 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Cliff Wickman <cpw@....com>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Jack Steiner <steiner@....com>, Mike Travis <travis@....com>
Subject: Re: [PATCH 3/3] x86: UV2 BAU hang workarounds


* Cliff Wickman <cpw@....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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