linux-kernel - Re: perfmon trouble

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Message-ID: <20180611171811.GB28292@bombadil.infradead.org>
Date:   Mon, 11 Jun 2018 10:18:11 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-ia64@...r.kernel.org
Subject: Re: perfmon trouble

On Mon, Jun 11, 2018 at 10:04:00AM -0700, Linus Torvalds wrote:
> On Mon, Jun 11, 2018 at 9:49 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > The problem is that even oprofile on ia64 depends on perfmon.
> 
> Hmm? You can definitely enable ia64 support for oprofile even without perfmon.

Oh, I think my memory is playing tricks on me.  This is my confusion, I think:

oprofile-$(CONFIG_PERFMON) += perfmon.o

so perfmon events are exposed through oprofile, but you can disable
perfmon without disabling oprofile.

> Because I'd be inclined to just remove CONFIG_PERFMON support, and see
> if anybody even notices..
> 
> I'm not expecting a lot of people to do a lot of oprofile on ia64
> anyway. It's a bit late to start optimizing things now.
> 
> Do people use perfmon still? Maybe. Maybe not. Perhaps we could just
> mark it as broken in the Kconfig file for now, and see if somebody
> says something?

That gets my vote.

Tony?  Fenghua?

diff --git a/arch/ia64/Kconfig b/arch/ia64/Kconfig
index 792437d526c6..ff861420b8f5 100644
--- a/arch/ia64/Kconfig
+++ b/arch/ia64/Kconfig
@@ -455,6 +455,7 @@ config IA64_MCA_RECOVERY
 
 config PERFMON
        bool "Performance monitor support"
+       depends on BROKEN
        help
          Selects whether support for the IA-64 performance monitor hardware
          is included in the kernel.  This makes some kernel data-structures a