Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <d5526090-0380-a586-40e1-7b3bb6fe6fb8@kernel.dk>
Date:   Fri, 2 Sep 2022 13:53:53 -0600
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:102.0) Gecko/20100101
 Thunderbird/102.1.2
Subject: Re: [RFC PATCH 00/30] Code tagging framework and applications
Content-Language: en-US
To:     Kent Overstreet <kent.overstreet@linux.dev>
Cc:     Roman Gushchin <roman.gushchin@linux.dev>,
        Yosry Ahmed <yosryahmed@google.com>,
        Michal Hocko <mhocko@suse.com>, Mel Gorman <mgorman@suse.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Johannes Weiner <hannes@cmpxchg.org>, dave@stgolabs.net,
        Matthew Wilcox <willy@infradead.org>, liam.howlett@oracle.com,
        void@manifault.com, juri.lelli@redhat.com, ldufour@linux.ibm.com,
        Peter Xu <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>, mcgrof@kernel.org,
        masahiroy@kernel.org, nathan@kernel.org, changbin.du@intel.com,
        ytcoode@gmail.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, Steven Rostedt <rostedt@goodmis.org>,
        bsegall@google.com, bristot@redhat.com, vschneid@redhat.com,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, 42.hyeyoo@gmail.com,
        glider@google.com, elver@google.com, dvyukov@google.com,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>, arnd@arndb.de,
        jbaron@akamai.com, David Rientjes <rientjes@google.com>,
        minchan@google.com, kaleshsingh@google.com,
        kernel-team@android.com, Linux-MM <linux-mm@kvack.org>,
        iommu@lists.linux.dev, kasan-dev@googlegroups.com,
        io-uring@vger.kernel.org, linux-arch@vger.kernel.org,
        xen-devel@lists.xenproject.org, linux-bcache@vger.kernel.org,
        linux-modules@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <20220831101948.f3etturccmp5ovkl@suse.de>
 <Yw88RFuBgc7yFYxA@dhcp22.suse.cz>
 <20220831190154.qdlsxfamans3ya5j@moria.home.lan>
 <CAJD7tkaev9B=UDYj2RL6pz-1454J8tv4gEr9y-2dnCksoLK0bw@mail.gmail.com>
 <YxExz+c1k3nbQMh4@P9FQF9L96D.corp.robot.car>
 <20220901223720.e4gudprscjtwltif@moria.home.lan>
 <YxE4BXw5i+BkxxD8@P9FQF9L96D.corp.robot.car>
 <20220902001747.qqsv2lzkuycffuqe@moria.home.lan>
 <YxFWrka+Wx0FfLXU@P9FQF9L96D.lan>
 <3a41b9fc-05f1-3f56-ecd0-70b9a2912a31@kernel.dk>
 <20220902194839.xqzgsoowous72jkz@moria.home.lan>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <20220902194839.xqzgsoowous72jkz@moria.home.lan>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 9/2/22 1:48 PM, Kent Overstreet wrote:
> On Fri, Sep 02, 2022 at 06:02:12AM -0600, Jens Axboe wrote:
>> On 9/1/22 7:04 PM, Roman Gushchin wrote:
>>> On Thu, Sep 01, 2022 at 08:17:47PM -0400, Kent Overstreet wrote:
>>>> On Thu, Sep 01, 2022 at 03:53:57PM -0700, Roman Gushchin wrote:
>>>>> I'd suggest to run something like iperf on a fast hardware. And maybe some
>>>>> io_uring stuff too. These are two places which were historically most sensitive
>>>>> to the (kernel) memory accounting speed.
>>>>
>>>> I'm getting wildly inconsistent results with iperf.
>>>>
>>>> io_uring-echo-server and rust_echo_bench gets me:
>>>> Benchmarking: 127.0.0.1:12345
>>>> 50 clients, running 512 bytes, 60 sec.
>>>>
>>>> Without alloc tagging:	120547 request/sec
>>>> With:			116748 request/sec
>>>>
>>>> https://github.com/frevib/io_uring-echo-server
>>>> https://github.com/haraldh/rust_echo_bench
>>>>
>>>> How's that look to you? Close enough? :)
>>>
>>> Yes, this looks good (a bit too good).
>>>
>>> I'm not that familiar with io_uring, Jens and Pavel should have a better idea
>>> what and how to run (I know they've workarounded the kernel memory accounting
>>> because of the performance in the past, this is why I suspect it might be an
>>> issue here as well).
>>
>> io_uring isn't alloc+free intensive on a per request basis anymore, it
>> would not be a good benchmark if the goal is to check for regressions in
>> that area.
> 
> Good to know. The benchmark is still a TCP benchmark though, so still useful.
> 
> Matthew suggested
>   while true; do echo 1 >/tmp/foo; rm /tmp/foo; done
> 
> I ran that on tmpfs, and the numbers with and without alloc tagging were
> statistically equal - there was a fair amount of variation, it wasn't a super
> controlled test, anywhere from 38-41 seconds with 100000 iterations (and alloc
> tagging was some of the faster runs).
> 
> But with memcg off, it ran in 32-33 seconds. We're piggybacking on the same
> mechanism memcg uses for stashing per-object pointers, so it looks like that's
> the bigger cost.

I've complained about memcg accounting before, the slowness of it is why
io_uring works around it by caching. Anything we account we try NOT do
in the fast path because of it, the slowdown is considerable.

You care about efficiency now? I thought that was relegated to
irrelevant 10M IOPS cases.

-- 
Jens Axboe