linux-kernel - Re: [patch 0/7] x86/pci: Switch to lockless ECAM configuration mode

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Message-ID: <20170627205521.GA764@bhelgaas-glaptop.roam.corp.google.com>
Date:   Tue, 27 Jun 2017 15:55:21 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Anvin <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        linux-pci@...r.kernel.org
Subject: Re: [patch 0/7] x86/pci: Switch to lockless ECAM configuration mode

[+cc linux-pci]

On Thu, Jun 22, 2017 at 12:28:09AM +0200, Thomas Gleixner wrote:
> Andi,
> 
> On Mon, 12 Jun 2017, Andi Kleen wrote:
> > On Thu, Mar 16, 2017 at 10:50:02PM +0100, Thomas Gleixner wrote:
> > > Andi reported that the Intel Uncore performance monitoring suffers from the
> > > global pci_lock which protects the generic PCI config space accessors.
> > > 
> > > This lock can be removed on X86 because all architecture specific config
> > > space accessors are either serialized by a seperate lock or can be
> > > converted to have their own locking. The mmconfig based access (ECAM) does
> > > not require serialization at the config read/write level because the access
> > > is a simple byte/word/dword read from or write to the memory mapped
> > > configuration space. In that case the lock does not provide any more
> > > protection than the hardware provides already.
> > > 
> > > The series converts the CE4100 PCI low level accessors to use the x86
> > > specific pci_config_lock and implements the switch over to lockless ECAM
> > > configureation space accesors when the system is capable.
> > 
> > What's the status of this patch series? The lock contention
> > problem is still there.
> 
> Just rechecked. It still applies and boots (patch 6/7) dropped.
> 
> If Bjorn has no objections I can route it through tip tomorrow.

Sorry for the delay.  I use patchwork as my to-do list, and it only
looks at linux-pci.  This series wasn't posted there, so I didn't see
it until now.

I have a couple trivial comments but I think it looks great overall.
Here's my ack if you want to apply it via tip:

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>

Bjorn