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From: David Gibson <david@gibson.dropbear.id.au>
To: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Cc: Greg Kurz <groug@kaod.org>,
	xiaoguangrong.eric@gmail.com, mst@redhat.com,
	imammedo@redhat.com, qemu-devel@nongnu.org, qemu-ppc@nongnu.org,
	linux-nvdimm@lists.01.org, aneesh.kumar@linux.ibm.com,
	kvm-ppc@vger.kernel.org, shivaprasadbhat@gmail.com,
	bharata@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org
Subject: Re: [RFC Qemu PATCH v2 1/2] spapr: drc: Add support for async hcalls at the drc level
Date: Mon, 8 Feb 2021 17:21:22 +1100	[thread overview]
Message-ID: <20210208062122.GA40668@yekko.fritz.box> (raw)
In-Reply-To: <3b47312a-217f-8df5-0bfd-1a653598abad@linux.ibm.com>

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On Tue, Jan 19, 2021 at 12:40:31PM +0530, Shivaprasad G Bhat wrote:
> Thanks for the comments!
> On 12/28/20 2:08 PM, David Gibson wrote:
> > On Mon, Dec 21, 2020 at 01:08:53PM +0100, Greg Kurz wrote:
> ...
> > > The overall idea looks good but I think you should consider using
> > > a thread pool to implement it. See below.
> > I am not convinced, however.  Specifically, attaching this to the DRC
> > doesn't make sense to me.  We're adding exactly one DRC related async
> > hcall, and I can't really see much call for another one.  We could
> > have other async hcalls - indeed we already have one for HPT resizing
> > - but attaching this to DRCs doesn't help for those.
> The semantics of the hcall made me think, if this is going to be
> re-usable for future if implemented at DRC level.

It would only be re-usable for operations that are actually connected
to DRCs.  It doesn't seem to me particularly likely that we'll ever
have more asynchronous hcalls that are also associated with DRCs.

> Other option
> is to move the async-hcall-state/list into the NVDIMMState structure
> in include/hw/mem/nvdimm.h and handle it with machine->nvdimms_state
> at a global level.

I'm ok with either of two options:

A) Implement this ad-hoc for this specific case, making whatever
simplifications you can based on this specific case.

B) Implement a general mechanism for async hcalls that is *not* tied
to DRCs.  Then use that for the existing H_RESIZE_HPT_PREPARE call as
well as this new one.

> Hope you are okay with using the pool based approach that Greg

Honestly a thread pool seems like it might be overkill for this

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_!

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  reply	other threads:[~2021-02-08  6:30 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-30 15:16 [RFC Qemu PATCH v2 0/2] spapr: nvdimm: Asynchronus flush hcall support Shivaprasad G Bhat
2020-11-30 15:16 ` [RFC Qemu PATCH v2 1/2] spapr: drc: Add support for async hcalls at the drc level Shivaprasad G Bhat
2020-12-21 12:08   ` Greg Kurz
2020-12-21 14:37     ` Greg Kurz
2020-12-28  8:38     ` David Gibson
2021-01-19  7:10       ` Shivaprasad G Bhat
2021-02-08  6:21         ` David Gibson [this message]
2021-03-23  7:53           ` Shivaprasad G Bhat
2020-11-30 15:17 ` [RFC Qemu PATCH v2 2/2] spapr: nvdimm: Implement async flush hcalls Shivaprasad G Bhat
2020-12-21 13:07   ` Greg Kurz
2020-12-21 13:07 ` [RFC Qemu PATCH v2 0/2] spapr: nvdimm: Asynchronus flush hcall support Greg Kurz

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