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

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Date:   Thu, 22 Jun 2017 00:28:09 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <ak@...ux.intel.com>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>, x86@...nel.org,
        Peter Anvin <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [patch 0/7] x86/pci: Switch to lockless ECAM configuration
 mode

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.

Thanks,

	tglx