From: Glenn Miles <milesg@linux.vnet.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: qemu-devel@nongnu.org,
"Daniel Henrique Barboza" <danielhb413@gmail.com>,
"Cédric Le Goater" <clg@kaod.org>,
"David Gibson" <david@gibson.dropbear.id.au>,
"Greg Kurz" <groug@kaod.org>,
"open list:PowerPC TCG CPUs" <qemu-ppc@nongnu.org>
Subject: Re: [PATCH 2/4] target/ppc: Add recording of taken branches to BHRB
Date: Thu, 21 Sep 2023 10:45:26 -0500 [thread overview]
Message-ID: <bd1fb03f3ec5a7da9201b1a20f146879@linux.vnet.ibm.com> (raw)
In-Reply-To: <955aa084c1e56559943f17514d7bed73@linux.vnet.ibm.com>
>> It all looks pretty good otherwise. I do worry about POWER8/9 which
>> do not have BHRB disable bit. How much do they slow down I wonder?
>
> That is a good question! I'll see if I can get some linux boot times
> with and without the changes on P9.
>
I ran some tests booting ubuntu 20.04 on the powrnv9 model and found
that it took about 5% longer to boot to the login prompt with the
changes than without. As discussed offline, I'll remove this support
from P8/P9 as the 5% reduction in performance is not worth the added
functionality. We could perhaps add it back in the future with a
command line option that has it disabled by default on P8/P9.
P10 and on has it disabled for non problem state branches, so we
should be good there.
Thanks,
Glenn
next prev parent reply other threads:[~2023-09-21 15:46 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-12 19:21 [PATCH 0/4] Add BHRB Facility Support Glenn Miles
2023-09-12 20:23 ` [PATCH 1/4] target/ppc: Add new hflags to support BHRB Glenn Miles
2023-09-15 0:39 ` Nicholas Piggin
2023-09-19 21:19 ` Glenn Miles
2023-09-12 20:24 ` [PATCH 2/4] target/ppc: Add recording of taken branches to BHRB Glenn Miles
2023-09-15 1:02 ` Nicholas Piggin
2023-09-19 21:35 ` Glenn Miles
2023-09-21 15:45 ` Glenn Miles [this message]
2023-09-12 20:24 ` [PATCH 3/4] target/ppc: Add clrbhrb and mfbhrbe instructions Glenn Miles
2023-09-15 1:13 ` Nicholas Piggin
2023-09-19 21:40 ` Glenn Miles
2023-09-12 20:25 ` [PATCH 4/4] target/ppc: Add migration support for BHRB Glenn Miles
2023-09-15 1:20 ` Nicholas Piggin
2023-09-19 22:01 ` Glenn Miles
2023-09-12 20:57 ` [PATCH 3/4] target/ppc: Add clrbhrb and mfbhrbe instructions Glenn Miles
2023-09-12 21:05 ` [PATCH 4/4] target/ppc: Add migration support for BHRB Glenn Miles
2023-09-12 21:27 ` Glenn Miles
-- strict thread matches above, loose matches on Subject: below --
2023-09-11 21:23 [PATCH 0/4] Add BHRB Facility Support Glenn Miles
2023-09-11 21:23 ` [PATCH 2/4] target/ppc: Add recording of taken branches to BHRB Glenn Miles
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