linux-kernel - Re: [PATCH v8 4/4] Kselftest for module text allocation benchmarking

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Message-Id: <20181106130557.11bfeddafe103bb609352aba@linux-foundation.org>
Date:   Tue, 6 Nov 2018 13:05:57 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     jeyu@...nel.org, willy@...radead.org, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kernel-hardening@...ts.openwall.com, daniel@...earbox.net,
        jannh@...gle.com, keescook@...omium.org, kristen@...ux.intel.com,
        dave.hansen@...el.com, arjan@...ux.intel.com
Subject: Re: [PATCH v8 4/4] Kselftest for module text allocation
 benchmarking

On Fri,  2 Nov 2018 12:25:20 -0700 Rick Edgecombe <rick.p.edgecombe@...el.com> wrote:

> This adds a test module in lib/, and a script in kselftest that does
> benchmarking on the allocation of memory in the module space. Performance here
> would have some small impact on kernel module insertions, BPF JIT insertions
> and kprobes. In the case of KASLR features for the module space, this module
> can be used to measure the allocation performance of different configurations.
> This module needs to be compiled into the kernel because module_alloc is not
> exported.

Well, we could export module_alloc().  Would that be helpful at all?

> With some modification to the code, as explained in the comments, it can be
> enabled to measure TLB flushes as well.
> 
> There are two tests in the module. One allocates until failure in order to
> test module capacity and the other times allocating space in the module area.
> They both use module sizes that roughly approximate the distribution of in-tree
> X86_64 modules.
> 
> You can control the number of modules used in the tests like this:
> echo m1000>/dev/mod_alloc_test
> 
> Run the test for module capacity like:
> echo t1>/dev/mod_alloc_test
> 
> The other test will measure the allocation time, and for CONFG_X86_64 and
> CONFIG_RANDOMIZE_BASE, also give data on how often the “backup area" is used.
> 
> Run the test for allocation time and backup area usage like:
> echo t2>/dev/mod_alloc_test
> The output will be something like this:
> num		all(ns)		last(ns)
> 1000		1083		1099
> Last module in backup count = 0
> Total modules in backup     = 0
> >1 module in backup count   = 0

Are the above usage instructions captured in the kernel code somewhere?
I can't see it, and expecting people to trawl git changelogs isn't
very friendly.