From: David Gibson <david@gibson.dropbear.id.au>
To: "Cédric Le Goater" <clg@kaod.org>
Cc: Gustavo Romero <gromero@linux.ibm.com>,
qemu-ppc@nongnu.org, qemu-devel@nongnu.org,
Greg Kurz <groug@kaod.org>
Subject: Re: [PATCH v2 0/6] spapr/xive: Activate StoreEOI in P10 compat guests
Date: Mon, 12 Oct 2020 16:38:46 +1100 [thread overview]
Message-ID: <20201012053846.GE4787@yekko.fritz.box> (raw)
In-Reply-To: <5a3af480-8e84-ddb8-e40e-e3050f6c2978@kaod.org>
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On Fri, Oct 09, 2020 at 07:57:32AM +0200, Cédric Le Goater wrote:
> On 10/9/20 2:23 AM, David Gibson wrote:
> > On Mon, Oct 05, 2020 at 06:51:41PM +0200, Cédric Le Goater wrote:
> >> Hello,
> >>
> >> When an interrupt has been handled, the OS notifies the interrupt
> >> controller with an EOI sequence. On the XIVE interrupt controller
> >> (POWER9 and POWER10), this can be done with a load or a store
> >> operation on the ESB interrupt management page of the interrupt. The
> >> StoreEOI operation has less latency and improves interrupt handling
> >> performance but it was deactivated during the POWER9 DD2.0 time-frame
> >> because of ordering issues. POWER9 systems use the LoadEOI instead.
> >> POWER10 has fixed the issue with a special load command which enforces
> >> Load-after-Store ordering and StoreEOI can be safely used.
> >
> > Do you mean that ordering is *always* enforced on P10? Or it's a
> > special form of load that has the ordering?
>
> It's a special form of load that has the ordering, only on available
> on P10. It's a no-op on P9.
no-op as in the load will have regular semantics, or as in the whole
load won't do anything?
I assume this meanse XIVE code needs to be updated to use that special
load for all accesses to XIVE registers...
> Linux commit b1f9be9392f0 ("powerpc/xive: Enforce load-after-store
> ordering when StoreEOI is active") introduced the Load-after-Store
> ordering offset and P10 support was added in the same 5.8 release.
.. which I guess this does?
> This is why StoreEOI should be advertised on P10 compat kernels only.
> I would have preferred to introduce some extra CAS bits. that would
> have been cleaner than mix the two.
Ok.
> The basic requirement is to advertise StoreEOI when the CPU compat
> allows it. I have used the capabilities to toggle the feature on/off.
> It seemed a clean way to cover all the extra needs :
>
> - switch it off on P10 if needed
> - switch it on on P9 for tests
Ok, seems reasonable
> > Also, weirdly, despite the series being addressed to me, only some of
> > the patches ended up in my inbox, rather than the list folder :/.
>
>
> Yes. I have received a few ot these :
>
> The original message was received at Mon, 5 Oct 2020 12:51:56 -0400
> from m0098419.ppops.net [127.0.0.1]
>
> ----- The following addresses had permanent fatal errors -----
> <david@gibson.dropbear.id.au>
Drat, I guess ozlabs.org fell off the net for a while.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2020-10-12 5:50 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-05 16:51 [PATCH v2 0/6] spapr/xive: Activate StoreEOI in P10 compat guests Cédric Le Goater
2020-10-05 16:51 ` [PATCH v2 1/6] spapr/xive: Introduce a StoreEOI capability Cédric Le Goater
2020-10-06 16:42 ` Greg Kurz
2020-10-07 5:59 ` Cédric Le Goater
2020-10-07 7:24 ` Greg Kurz
2020-10-05 16:51 ` [PATCH v2 2/6] spapr/xive: Add a warning when StoreEOI is activated on POWER8 CPUs Cédric Le Goater
2020-10-06 16:52 ` Greg Kurz
2020-10-05 16:51 ` [PATCH v2 3/6] spapr/xive: Add a warning when StoreEOI is activated on POWER9 CPUs Cédric Le Goater
2020-10-06 16:58 ` Greg Kurz
2020-10-06 17:03 ` Cédric Le Goater
2020-10-07 8:56 ` Greg Kurz
2020-10-07 9:21 ` Cédric Le Goater
2020-10-05 16:51 ` [PATCH v2 4/6] spapr/xive: Enforce load-after-store ordering Cédric Le Goater
2020-10-06 17:02 ` Greg Kurz
2020-10-05 16:51 ` [PATCH v2 5/6] spapr/xive: Activate StoreEOI at the source level Cédric Le Goater
2020-10-06 17:06 ` Greg Kurz
2020-10-06 17:41 ` Cédric Le Goater
2020-10-07 7:26 ` Greg Kurz
2020-10-05 16:51 ` [PATCH v2 6/6] spapr/xive: Introduce a new CAS value for the StoreEOI capability Cédric Le Goater
2020-10-06 17:39 ` Greg Kurz
2020-10-06 17:56 ` Cédric Le Goater
2020-10-07 13:43 ` Greg Kurz
2020-10-07 14:28 ` Cédric Le Goater
2020-10-09 0:23 ` [PATCH v2 0/6] spapr/xive: Activate StoreEOI in P10 compat guests David Gibson
2020-10-09 5:57 ` Cédric Le Goater
2020-10-12 5:38 ` David Gibson [this message]
2020-11-02 13:22 ` Cédric Le Goater
2020-11-23 6:44 ` David Gibson
2020-11-23 11:16 ` Cédric Le Goater
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