From: Michael Kelley <mhklinux@outlook.com>
To: "Kuppuswamy Sathyanarayanan"
<sathyanarayanan.kuppuswamy@linux.intel.com>,
"Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
Cc: "haiyangz@microsoft.com" <haiyangz@microsoft.com>,
"wei.liu@kernel.org" <wei.liu@kernel.org>,
"decui@microsoft.com" <decui@microsoft.com>,
"lpieralisi@kernel.org" <lpieralisi@kernel.org>,
"kw@linux.com" <kw@linux.com>,
"robh@kernel.org" <robh@kernel.org>,
"bhelgaas@google.com" <bhelgaas@google.com>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>
Subject: RE: [PATCH 1/1] PCI: hv: Fix ring buffer size calculation
Date: Thu, 15 Feb 2024 07:26:38 +0000 [thread overview]
Message-ID: <SN6PR02MB415746AAB8228DD1E10B5D41D44D2@SN6PR02MB4157.namprd02.prod.outlook.com> (raw)
In-Reply-To: <12efa165-b4bb-40ae-ac38-deedceba7b27@linux.intel.com>
From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>
> On 2/12/24 10:19 PM, mhkelley58@gmail.com wrote:
> > From: Michael Kelley <mhklinux@outlook.com>
> >
> > For a physical PCI device that is passed through to a Hyper-V guest VM,
> > current code specifies the VMBus ring buffer size as 4 pages. But this
> > is an inappropriate dependency, since the amount of ring buffer space
> > needed is unrelated to PAGE_SIZE. For example, on x86 the ring buffer
> > size ends up as 16 Kbytes, while on ARM64 with 64 Kbyte pages, the ring
> > size bloats to 256 Kbytes. The ring buffer for PCI pass-thru devices
> > is used for only a few messages during device setup and removal, so any
> > space above a few Kbytes is wasted.
> >
> > Fix this by declaring the ring buffer size to be a fixed 16 Kbytes.
> > Furthermore, use the VMBUS_RING_SIZE() macro so that the ring buffer
> > header is properly accounted for, and so the size is rounded up to a
> > page boundary, using the page size for which the kernel is built. While
> > w/64 Kbyte pages this results in a 64 Kbyte ring buffer header plus a
> > 64 Kbyte ring buffer, that's the smallest possible with that page size.
> > It's still 128 Kbytes better than the current code.
> >
> > Cc: <stable@vger.kernel.org> # 5.15.x
> > Signed-off-by: Michael Kelley <mhklinux@outlook.com>
> > ---
> Looks good to me.
>
> Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > drivers/pci/controller/pci-hyperv.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index 1eaffff40b8d..5f22ad38bb98 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -465,7 +465,7 @@ struct pci_eject_response {
> > u32 status;
> > } __packed;
> >
> > -static int pci_ring_size = (4 * PAGE_SIZE);
> > +static int pci_ring_size = VMBUS_RING_SIZE(16 * 1024);
> >
> Nit: I think you can use SZ_16K to make it more readable.
Thanks for the review. I'll send a v2 that uses SZ_16K per your
and Ilpo Järvinen's comment.
Michael
next prev parent reply other threads:[~2024-02-15 7:26 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-13 6:19 [PATCH 1/1] PCI: hv: Fix ring buffer size calculation mhkelley58
2024-02-13 6:54 ` Kuppuswamy Sathyanarayanan
2024-02-15 7:26 ` Michael Kelley [this message]
2024-02-14 14:18 ` Ilpo Järvinen
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