From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Ajay Kaher <akaher@vmware.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
Srivatsa Bhat <srivatsab@vmware.com>,
"srivatsa@csail.mit.edu" <srivatsa@csail.mit.edu>,
Alexey Makhalov <amakhalov@vmware.com>,
Vasavi Sirnapalli <vsirnapalli@vmware.com>,
"er.ajay.kaher@gmail.com" <er.ajay.kaher@gmail.com>,
"willy@infradead.org" <willy@infradead.org>,
Nadav Amit <namit@vmware.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
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"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
Alexander Graf <graf@amazon.com>
Subject: Re: [PATCH v2] x86/PCI: Prefer MMIO over PIO on all hypervisor
Date: Mon, 03 Oct 2022 17:03:41 +0200 [thread overview]
Message-ID: <87tu4l9cfm.fsf@redhat.com> (raw)
In-Reply-To: <B64FD502-E794-4E94-A267-D690476C57EE@vmware.com>
Ajay Kaher <akaher@vmware.com> writes:
>> On 13/09/22, 7:05 PM, "Vitaly Kuznetsov" <vkuznets@redhat.com> wrote:
>>>
>>> Thanks Vitaly for your response.
>>>
>>> 1. we have multiple objects of struct pci_raw_ops, 2. adding 'priority' field to struct pci_raw_ops
>>> doesn't seems to be appropriate as need to take decision which object of struct pci_raw_ops has
>>> to be used, not something with-in struct pci_raw_ops.
>>
>> I'm not sure I follow, you have two instances of 'struct pci_raw_ops'
>> which are called 'raw_pci_ops' and 'raw_pci_ext_ops'. What if you do
>> something like (completely untested):
>>
>> diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
>> index 70533fdcbf02..fb8270fa6c78 100644
>> --- a/arch/x86/include/asm/pci_x86.h
>> +++ b/arch/x86/include/asm/pci_x86.h
>> @@ -116,6 +116,7 @@ extern void (*pcibios_disable_irq)(struct pci_dev *dev);
>> extern bool mp_should_keep_irq(struct device *dev);
>>
>> struct pci_raw_ops {
>> + int rating;
>> int (*read)(unsigned int domain, unsigned int bus, unsigned int devfn,
>> int reg, int len, u32 *val);
>> int (*write)(unsigned int domain, unsigned int bus, unsigned int devfn,
>> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
>> index ddb798603201..e9965fd11576 100644
>> --- a/arch/x86/pci/common.c
>> +++ b/arch/x86/pci/common.c
>> @@ -40,7 +40,8 @@ const struct pci_raw_ops *__read_mostly raw_pci_ext_ops;
>> int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
>> int reg, int len, u32 *val)
>> {
>> - if (domain == 0 && reg < 256 && raw_pci_ops)
>> + if (domain == 0 && reg < 256 && raw_pci_ops &&
>> + (!raw_pci_ext_ops || raw_pci_ext_ops->rating <= raw_pci_ops->rating))
>> return raw_pci_ops->read(domain, bus, devfn, reg, len, val);
>> if (raw_pci_ext_ops)
>> return raw_pci_ext_ops->read(domain, bus, devfn, reg, len, val);
>> @@ -50,7 +51,8 @@ int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
>> int raw_pci_write(unsigned int domain, unsigned int bus, unsigned int devfn,
>> int reg, int len, u32 val)
>> {
>> - if (domain == 0 && reg < 256 && raw_pci_ops)
>> + if (domain == 0 && reg < 256 && raw_pci_ops &&
>> + (!raw_pci_ext_ops || raw_pci_ext_ops->rating <= raw_pci_ops->rating))
>> return raw_pci_ops->write(domain, bus, devfn, reg, len, val);
>> if (raw_pci_ext_ops)
>> return raw_pci_ext_ops->write(domain, bus, devfn, reg, len, val);
>>
>> and then somewhere in Vmware hypervisor initialization code
>> (arch/x86/kernel/cpu/vmware.c) you do
>>
>> raw_pci_ext_ops->rating = 100;
>
> Thanks Vitaly, for your review and helping us to improve the code.
>
> I was working to make changes as you suggested, but before sending v3 would like to
> discuss on following:
>
> If we add rating with-in struct pci_raw_ops then we can't have pci_mmcfg as const,
> and following change is must in arch/x86/pci/mmconfig_64.c:
>
> -const struct pci_raw_ops pci_mmcfg = {
> +struct pci_raw_ops pci_mmcfg = {
> .read = pci_mmcfg_read,
> .write = pci_mmcfg_write,
> };
>
> So to avoid this change, is it fine to have global bool prefer_raw_pci_ext_ops?
>
> And raw_pci_read() will have following change:
>
> - if (domain == 0 && reg < 256 && raw_pci_ops)
> + if (domain == 0 && reg < 256 && raw_pci_ops &&
> + (!prefer_raw_pci_ext_ops || !raw_pci_ext_ops)
>
Not my but rather PCI maintainer's call but IMHO dropping 'const' is
better, introducing a new global var is our 'last resort' and should be
avoided whenever possible. Alternatively, you can add a
raw_pci_ext_ops_preferred() function checking somethin within 'struct
hypervisor_x86' but I'm unsure if it's better.
Also, please check Alex' question/suggestion.
...
--
Vitaly
next prev parent reply other threads:[~2022-10-03 15:03 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 12:47 [PATCH v2] x86/PCI: Prefer MMIO over PIO on all hypervisor Ajay Kaher
2022-09-13 13:34 ` Vitaly Kuznetsov
2022-09-29 5:36 ` Ajay Kaher
2022-09-29 9:12 ` Alexander Graf
2022-10-03 15:03 ` Vitaly Kuznetsov [this message]
2022-10-03 17:34 ` Nadav Amit
2022-10-03 21:06 ` H. Peter Anvin
2022-10-03 21:28 ` Nadav Amit
2022-10-03 23:51 ` H. Peter Anvin
2022-10-04 0:19 ` Nadav Amit
2022-10-04 8:22 ` Alexander Graf
2022-10-04 18:48 ` Nadav Amit
2022-10-10 14:58 ` Nadav Amit
2022-10-10 17:05 ` Michael S. Tsirkin
2022-10-04 8:30 ` Vitaly Kuznetsov
2022-10-03 21:01 ` H. Peter Anvin
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