From: Greg KH <gregkh@linuxfoundation.org>
To: Ajay Kaher <akaher@vmware.com>
Cc: bhelgaas@google.com, tglx@linutronix.de, mingo@redhat.com,
bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org,
hpa@zytor.com, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org,
rostedt@goodmis.org, namit@vmware.com, srivatsab@vmware.com,
srivatsa@csail.mit.edu, amakhalov@vmware.com, anishs@vmware.com,
vsirnapalli@vmware.com, er.ajay.kaher@gmail.com
Subject: Re: [PATCH] MMIO should have more priority then IO
Date: Wed, 29 Jun 2022 08:12:41 +0200 [thread overview]
Message-ID: <YrvtWVqj/w8V5nIJ@kroah.com> (raw)
In-Reply-To: <1656433761-9163-1-git-send-email-akaher@vmware.com>
On Tue, Jun 28, 2022 at 09:59:21PM +0530, Ajay Kaher wrote:
> Port IO instructions (PIO) are less efficient than MMIO (memory
> mapped I/O). They require twice as many PCI accesses and PIO
> instructions are serializing. As a result, MMIO should be preferred
> when possible over PIO.
>
> Bare metal test result
> 1 million reads using raw_pci_read() took:
> PIO: 0.433153 Sec.
> MMIO: 0.268792 Sec.
>
> Virtual Machine test result
> 1 hundred thousand reads using raw_pci_read() took:
> PIO: 12.809 Sec.
> MMIO: took 8.517 Sec.
>
> Signed-off-by: Ajay Kaher <akaher@vmware.com>
> ---
> arch/x86/pci/common.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> index 3507f456f..0b3383d9c 100644
> --- a/arch/x86/pci/common.c
> +++ b/arch/x86/pci/common.c
> @@ -40,20 +40,20 @@ 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 (raw_pci_ext_ops)
> + return raw_pci_ext_ops->read(domain, bus, devfn, reg, len, val);
> if (domain == 0 && reg < 256 && raw_pci_ops)
> 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);
> return -EINVAL;
> }
>
> int raw_pci_write(unsigned int domain, unsigned int bus, unsigned int devfn,
> int reg, int len, u32 val)
> {
> + if (raw_pci_ext_ops)
> + return raw_pci_ext_ops->write(domain, bus, devfn, reg, len, val);
> if (domain == 0 && reg < 256 && raw_pci_ops)
> 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);
> return -EINVAL;
> }
>
> --
> 2.30.0
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
next prev parent reply other threads:[~2022-06-29 6:12 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-28 16:29 [PATCH] MMIO should have more priority then IO Ajay Kaher
2022-06-28 18:09 ` Bjorn Helgaas
2022-07-08 5:56 ` Ajay Kaher
2022-07-08 12:56 ` Matthew Wilcox
2022-07-08 16:45 ` Nadav Amit
2022-07-08 17:55 ` Matthew Wilcox
2022-07-08 18:35 ` Nadav Amit
2022-07-08 18:43 ` Matthew Wilcox
2022-07-08 19:49 ` Nadav Amit
2022-07-11 6:31 ` Ajay Kaher
2022-07-11 17:04 ` Nadav Amit
2022-07-11 17:53 ` Ajay Kaher
2022-07-11 18:18 ` H. Peter Anvin
2022-07-11 19:43 ` Paolo Bonzini
2022-07-12 21:20 ` Shuah Khan
2022-08-31 21:44 ` Matthew Wilcox
2022-08-31 22:23 ` Shuah Khan
2022-06-29 6:12 ` Greg KH [this message]
2022-06-29 6:37 ` H. Peter Anvin
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