From: Paul Mackerras <paulus@ozlabs.org>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: aik@ozlabs.ru, benh@kernel.crashing.org,
bharata@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
michael@ellerman.id.au
Subject: Re: [RFCv3 00/17] PAPR HPT resizing, guest & host side
Date: Thu, 25 Aug 2016 22:38:34 +1000 [thread overview]
Message-ID: <20160825123834.GB4815@fergus.ozlabs.ibm.com> (raw)
In-Reply-To: <1458532404-21258-1-git-send-email-david@gibson.dropbear.id.au>
On Mon, Mar 21, 2016 at 02:53:07PM +1100, David Gibson wrote:
> This is an implementation of the kernel parts of the PAPR hashed page
> table (HPT) resizing extension.
>
> It contains a complete guest-side implementation - or as complete as
> it can be until we have a final PAPR change.
>
> It also contains a draft host side implementation for KVM HV (the KVM
> PR and TCG host-side implementations live in qemu). This works, but
> is very slow in the critical section (where the guest must be
> stopped). It is significantly slower than the TCG/PR implementation;
> unusably slow for large hash tables (~2.8s for a 1G HPT).
>
> I'm still looking into what's the cause of the slowness, and I'm not
> sure yet if the current approach can be tweaked to be fast enough, or
> if it will require a new approach.
I have finally managed to have a close look at this series. The
approach and implementation seem basically sane, though I think the
rehash function could be optimized a bit. I also have an optimized
implementation of hpte_page_size() and hpte_base_page_size() which
should be a lot quicker than the 2d linear (areal?) search which we do
at present.
Paul.
next prev parent reply other threads:[~2016-08-25 12:38 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-21 3:53 [RFCv3 00/17] PAPR HPT resizing, guest & host side David Gibson
2016-03-21 3:53 ` [RFCv3 01/17] pseries: Add hypercall wrappers for hash page table resizing David Gibson
2016-03-21 3:53 ` [RFCv3 02/17] pseries: Add support for hash " David Gibson
2016-03-21 3:53 ` [RFCv3 03/17] pseries: Advertise HPT resizing support via CAS David Gibson
2016-03-21 3:53 ` [RFCv3 04/17] pseries: Automatically resize HPT for memory hot add/remove David Gibson
2016-03-21 3:53 ` [RFCv3 05/17] powerpc/kvm: Corectly report KVM_CAP_PPC_ALLOC_HTAB David Gibson
2016-03-21 3:53 ` [RFCv3 06/17] powerpc/kvm: Add capability flag for hashed page table resizing David Gibson
2016-03-21 3:53 ` [RFCv3 07/17] powerpc/kvm: Rename kvm_alloc_hpt() for clarity David Gibson
2016-03-21 3:53 ` [RFCv3 08/17] powerpc/kvm: Gather HPT related variables into sub-structure David Gibson
2016-03-21 3:53 ` [RFCv3 09/17] powerpc/kvm: Don't store values derivable from HPT order David Gibson
2016-03-21 3:53 ` [RFCv3 10/17] powerpc/kvm: Split HPT allocation from activation David Gibson
2016-03-21 3:53 ` [RFCv3 11/17] powerpc/kvm: Allow KVM_PPC_ALLOCATE_HTAB ioctl() to change HPT size David Gibson
2016-03-21 3:53 ` [RFCv3 12/17] powerpc/kvm: Create kvmppc_unmap_hpte_helper() David Gibson
2016-03-21 3:53 ` [RFCv3 13/17] powerpc/kvm: KVM-HV HPT resizing stub implementation David Gibson
2016-03-21 3:53 ` [RFCv3 14/17] powerpc/kvm: Outline of KVM-HV HPT resizing implementation David Gibson
2016-03-21 3:53 ` [RFCv3 15/17] powerpc/kvm: KVM-HV HPT resizing, preparation path David Gibson
2016-03-21 3:53 ` [RFCv3 16/17] powerpc/kvm: HVM-HV HPT resizing, commit path David Gibson
2016-03-21 3:53 ` [RFCv3 17/17] powerpc/kvm: Advertise availablity of HPT resizing on KVM HV David Gibson
2016-03-21 5:46 ` [RFCv3 00/17] PAPR HPT resizing, guest & host side David Gibson
2016-08-25 12:38 ` Paul Mackerras [this message]
2016-08-25 17:57 ` David Gibson
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