linux-kernel - Re: [PATCH] s390/oprofile: Remove deprecated create

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Date:	Tue, 14 Jun 2016 07:36:08 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Robert Richter <rric@...nel.org>
Cc:	Bhaktipriya Shridhar <bhaktipriya96@...il.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Tejun Heo <tj@...nel.org>, oprofile-list@...ts.sf.net,
	linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Andreas Krebbel <krebbel@...ux.vnet.ibm.com>,
	Andreas Arnez <arnez@...ux.vnet.ibm.com>,
	William Cohen <wcohen@...hat.com>
Subject: Re: [PATCH] s390/oprofile: Remove deprecated create_workqueue

On Mon, Jun 13, 2016 at 06:29:14PM +0200, Robert Richter wrote:
> Heiko,
> 
> On 09.06.16 11:00:56, Heiko Carstens wrote:
> > However I'm wondering if we shouldn't simply remove at least the s390
> > specific hwswampler code from the oprofile module. This would still leave
> > the common code timer based sampling mode for oprofile working on s390.
> > 
> > It looks like the oprofile user space utility nowadays (since 2012) uses
> > the kernel perf interface instead of the oprofile interface anyway, if
> > present. So the oprofile module itself doesn't seem to have too many users
> > left.
> > 
> > Any opinions?
> 
> yes, the kernel driver is not necessary for oprofile userland for a
> while now. There is no ongoing development any longer, most patches
> are due to changes in the kernel apis.
> 
> So if there is code that needs a larger rework due to other kernel
> changes and there is no user anymore, I am fine with removing the code
> instead of reworking it. I still would just keep existing code as long
> as we can keep it unchanged (some like the lightwight of oprofile,
> esp. in the embedded space). If there is a user of the code, a
> Tested-by would be good for new code changes.
> 
> If there are users of the hwswampler, speak up now. Else, let's just
> remove it.

Ok, so I'll wait a week or so and remove the code if nobody speaks up. Is
it ok for you if I add the patch to the s390 kernel tree?
The patch would only remove s390 specific architecture code.

I have this pending:

    s390/oprofile: remove hardware sampler support
    
    Remove hardware sampler support from oprofile module.
    
    The oprofile user space utilty has been switched to use the kernel
    perf interface, for which we also provide hardware sampling support.
    
    In addition the hardware sampling support is also slightly broken: it
    supports only 16 bits for the pid and therefore would generate wrong
    results on machines which have a pid >64k.
    
    Also the pt_regs structure which was passed to oprofile common code
    cannot necessarily be used to generate sane backtraces, since the
    task(s) in question may run while the samples are fed to oprofile.
    So the result would be more or less random.
    
    However given that the only user space tools switched to the perf
    interface already four years ago the hardware sampler code seems to be
    unused code, and therefore it should be reasonable to remove it.
    
    The timer based oprofile support continues to work.
    
    Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>

 Documentation/kernel-parameters.txt |    2 -
 arch/s390/oprofile/Makefile         |    1 -
 arch/s390/oprofile/hwsampler.c      | 1178 --------------------------------
 arch/s390/oprofile/hwsampler.h      |   63 --
 arch/s390/oprofile/init.c           |  489 -------------
 arch/s390/oprofile/op_counter.h     |   21 -
 6 files changed, 1754 deletions(-)