From: Scott Wood <scottwood@freescale.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Laurentiu Tudor <Laurentiu.Tudor@freescale.com>,
linuxppc-dev@lists.ozlabs.org, Stuart Yoder <b08248@gmail.com>
Subject: Re: [PATCH] powerpc/booke64: Configurable lazy interrupt disabling
Date: Mon, 23 Jan 2012 13:31:35 -0600 [thread overview]
Message-ID: <4F1DB597.7030506@freescale.com> (raw)
In-Reply-To: <1327100531.2923.3.camel@pasglop>
On 01/20/2012 05:02 PM, Benjamin Herrenschmidt wrote:
>
>> With Topaz, interrupts go directly to guests and we don't want to require a
>> trap/hcall to do an IACK, as that adds potentially thousands of cycles of
>> latency to every interrupt.
>>
>> As you know, with external proxy interrupts are acknowledged by the
>> hardware and it becomes problematic to replay the interrupt in
>> the context of lazy EE when interrupts are re-enabled. The interrupt
>> will not fire again when you enable EE.
>
> So you have a broken HW and broken HV design to start with ... :-)
That "breakage" significantly reduces the overhead of handling
interrupts in a guest, since we don't need to involve the hypervisor (at
least on the entry side -- there's a hack to avoid it on EOI as well,
though that involves exposing some MPIC registers directly; users can
decide whether it's worth enabling for their use case).
-Scott
prev parent reply other threads:[~2012-01-23 19:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-18 14:35 [PATCH] powerpc/booke64: Configurable lazy interrupt disabling Laurentiu Tudor
2012-01-18 21:10 ` Benjamin Herrenschmidt
2012-01-19 13:18 ` Tudor Laurentiu
2012-01-19 19:21 ` Stuart Yoder
2012-01-19 19:29 ` Stuart Yoder
2012-01-20 23:05 ` Benjamin Herrenschmidt
2012-01-23 19:21 ` Scott Wood
2012-01-23 20:50 ` Benjamin Herrenschmidt
2012-01-25 14:32 ` Tudor Laurentiu
2012-01-30 21:47 ` Scott Wood
2012-01-30 22:15 ` Benjamin Herrenschmidt
2012-01-30 23:13 ` Scott Wood
2012-01-20 23:02 ` Benjamin Herrenschmidt
2012-01-23 19:31 ` Scott Wood [this message]
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