Message-ID: <aFOLIO9JReglmE+3@phytium.com.cn>
Date: Thu, 19 Jun 2025 11:59:28 +0800
From: Yuquan Wang <wangyuquan1236@...tium.com.cn>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Neeraj Kumar <s.neeraj@...sung.com>, linux-cxl@...r.kernel.org,
	linux-mm@...ck.org, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, linuxarm@...wei.com,
	tongtiangen@...wei.com, Yicong Yang <yangyicong@...wei.com>,
	Niyas Sait <niyas.sait@...wei.com>, ajayjoshi@...ron.com,
	Vandana Salve <vsalve@...ron.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Dave Jiang <dave.jiang@...el.com>,
	Alison Schofield <alison.schofield@...el.com>,
	Ira Weiny <ira.weiny@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Gregory Price <gourry@...rry.net>,
	Huang Ying <ying.huang@...el.com>, Vishak G <vishak.g@...sung.com>,
	Krishna Kanth Reddy <krish.reddy@...sung.com>,
	Alok Rathore <alok.rathore@...sung.com>, gost.dev@...sung.com
Subject: Re: [RFC PATCH 0/4] CXL Hotness Monitoring Unit perf driver

On Wed, Jan 15, 2025 at 01:42:07PM +0000, Jonathan Cameron wrote:
> On Fri, 3 Jan 2025 10:57:22 +0530
> Neeraj Kumar <s.neeraj@...sung.com> wrote:
> 
> > On 27/11/24 04:34PM, Jonathan Cameron wrote:
> > >On Thu, 21 Nov 2024 10:18:41 +0000
> > >Jonathan Cameron <Jonathan.Cameron@...wei.com> wrote:
> > >  
> > >> The CXL specification release 3.2 is now available under a click through at
> > >> https://computeexpresslink.org/cxl-specification/ and it brings new
> > >> shiny toys.  
> > >
> > >If anyone wants to play, basic emulation on my CXL QEMU staging tree
> > >https://gitlab.com/jic23/qemu/-/commit/e89b35d264c1bcc04807e7afab1254f35ffc8cb9
> > >
> > >Branch with a few other things on top is:
> > >https://gitlab.com/jic23/qemu/-/commits/cxl-2024-11-27
> > >
> > >Note that this currently doesn't produce real data.  I have a plan
> > >/ initial PoC / hack to hook that up via an addition to the QEMU cache
> > >plugin and an external tool to emulate the hotness tracker counting
> > >hardware. Will be a little while before I get that finished, so in
> > >a meantime the above exercises the driver.
> > >
> > >Jonathan
> > >  
> > >>
> > >> RFC reason
> > >> - Whilst trace capture with a particular configuration is potentially useful
> > >>   the intent is that CXL HMU units will be used to drive various forms of
> > >>   hotpage migration for memory tiering setups. This driver doesn't do this
> > >>   (yet), but rather provides data capture etc for experimentation and
> > >>   for working out how to mostly put the allocations in the right place to
> > >>   start with by tuning applications.
> > >>
> > >> CXL r3.2 introduces a CXL Hotness Monitoring Unit definition. The intent
> > >> of this is to provide a way to establish which units of memory (typically
> > >> pages or larger) in CXL attached memory are hot. The implementation details
> > >> and algorithm are all implementation defined. The specification simply
> > >> describes the 'interface' which takes the form of ring buffer of hotness
> > >> records in a PCI BAR and defined capability, configuration and status
> > >> registers.
> > >>
> > >> The hardware may have constraints on what it can track, granularity etc
> > >> and on how accurately it tracks (e.g. counter exhaustion, inaccurate
> > >> trackers). Some of these constraints are discoverable from the hardware
> > >> registers, others such as loss of accuracy have no universally accepted
> > >> measures as they are typically access pattern dependent. Sadly it is
> > >> very unlikely any hardware will implement a truly precise tracker given
> > >> the large resource requirements for tracking at a useful granularity.
> > >>
> > >> There are two fundamental operation modes:
> > >>
> > >> * Epoch based. Counters are checked after a period of time (Epoch) and
> > >>   if over a threshold added to the hotlist.
> > >> * Always on. Counters run until a threshold is reached, after that the
> > >>   hot unit is added to the hotlist and the counter released.
> > >>
> > >> Counting can be filtered on:
> > >>
> > >> * Region of CXL DPA space (256MiB per bit in a bitmap).
> > >> * Type of access - Trusted and non trusted or non trusted only, R/W/RW
> > >>
> > >> Sampling can be modified by:
> > >>
> > >> * Downsampling including potentially randomized downsampling.
> > >>
> > >> The driver presented here is intended to be useful in its own right but
> > >> also to act as the first step of a possible path towards hotness monitoring
> > >> based hot page migration. Those steps might look like.
> > >>
> > >> 1. Gather data - drivers provide telemetry like solutions to get that
> > >>    data. May be enhanced, for example in this driver by providing the
> > >>    HPA address rather than DPA Unit Address. Userspace can access enough
> > >>    information to do this so maybe not.
> > >> 2. Userspace algorithm development, possibly combined with userspace
> > >>    triggered migration by PA. Working out how to use different levels
> > >>    of constrained hardware resources will be challenging.
> > >> 3. Move those algorithms in kernel. Will require generalization across
> > >>    different hotpage trackers etc.
> > >>
> > >> So far this driver just gives access to the raw data. I will probably kick
> > >> of a longer discussion on how to do adaptive sampling needed to actually
> > >> use these units for tiering etc, sometime soon (if no one one else beats
> > >> me too it).  There is a follow up topic of how to virtualize this stuff
> > >> for memory stranding cases (VM gets a fixed mixture of fast and slow
> > >> memory and should do it's own tiering).
> > >>
> > >> More details in the Documentation patch but typical commands are:
> > >>
> > >> $perf record -a  -e cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,\
> > >>  hotness_threshold=1024,epoch_multiplier=4,epoch_scale=4,range_base=0,\
> > >>  range_size=1024,randomized_downsampling=0,downsampling_factor=32,\
> > >>  hotness_granual=12  
> > 
> > Facing issue while executing perf record on x86 emulation environment using following steps
> > 
> > 1. Tried applying CHMU Patch on branch cxl-for-6.13 using b4 utility. As
> > base commit is not specified, with minor change able to apply patch.
> > Compiled kernel with CONFIG_CXL_HMU
> > 
> > 2. Compiled jic23/cxl-2024-11-27 for x86_64-softmmu
> > 
> > 3. Launched Qemu with following CXL topology along with compiled kernel
> > VM="-object memory-backend-ram,id=vmem1,share=on,size=512M \
> >      -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
> >      -device cxl-rp,port=0,bus=cxl.1,id=root_port13,chassis=0,slot=2 \
> >      -device cxl-type3,bus=root_port13,volatile-memdev=vmem1,id=cxl-vmem1 \
> >      -M cxl-fmw.0.targets.0=cxl.1,cxl-fmw.0.size=4G,cxl-fmw.0.interleave-granularity=8k"
> > 
> > 4. Created region and onlined this memory. Also run top utility on the newly created 
> > numa node using numactl -m<node> top
> > 
> > 5. Compiled and installed perf utility in qemu environment, and able to
> > see cxl_hmu_mem* entries in perf list
> > 
> > root@...UCXL2030mm:~# perf list
> > <snip>
> >   cxl_hmu_mem0.0.0/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_hmu_mem0.0.1/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_hmu_mem0.0.2/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_hmu_mem1.0.0/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_hmu_mem1.0.1/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_hmu_mem1.0.2/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw ev>
> >   cxl_pmu_mem0.0/vid=0..0xffff,edge,mask=0..0xffffffff,.../modifier[Raw event descriptor]
> >   cxl_pmu_mem0.1/vid=0..0xffff,edge,mask=0..0xffffffff,.../modifier[Raw event descriptor]
> >   cxl_pmu_mem1.0/vid=0..0xffff,edge,mask=0..0xffffffff,.../modifier[Raw event descriptor]
> >   cxl_pmu_mem1.1/vid=0..0xffff,edge,mask=0..0xffffffff,.../modifier[Raw event descriptor]
> > <snip>
> > 
> > 6. Tried running perf command mentioned in Documentation/trace/cxl-hmu.rst
> > 
> > root@...UCXL2030mm:/home/cxl/cxl-linux-mainline/tools/perf# perf -v
> > perf version 6.12.rc5.gc198a4f4a356
> > root@...UCXL2030mm:/home/cxl/cxl-linux-mainline/tools/perf# perf record -a  -e cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,hotness_threshold=1024,epoch_multiplier=4,epoch_scale=4,range_base=0,range_size=1024,randomized_downsampling=0,downsampling_factor=32,hotness_granual=12
> > event syntax error: '..ess_granual=12'
> >                                   \___ Unrecognized input
> 
> This is probably my mistake when cutting and pasting the example from a terminal.
> Add a trailing / and something to run.
> 
>  perf record -a  -e cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,hotness_threshold=1024,epoch_multiplier=4,epoch_scale=4,range_base=0,range_size=1024,randomized_downsampling=0,downsampling_factor=32,hotness_granual=12/ -- sleep 10

Hi Jonathan,

I tried to use this new command but perf shows error. 

Based on the change of hmu iomap_block size[1], my steps are like below:

step1: Create cxl region and online the numa node

root@...ntu-jammy-arm64:~/tools# numactl -H
available: 3 nodes (0-2)
node 0 cpus: 0 1
node 0 size: 1972 MB
node 0 free: 1694 MB
node 1 cpus: 2 3
node 1 size: 1942 MB
node 1 free: 1690 MB
node 2 cpus:
node 2 size: 256 MB
node 2 free: 256 MB
node distances:
node   0   1   2
  0:  10  20  20
  1:  20  10  20
  2:  20  20  10

step2: Bind this numa node to run 'ls'

root@...ntu-jammy-arm64:~/tools# numactl -m 2 ls
build   perf.data  ndctl  perf     

root@...ntu-jammy-arm64:~/tools# numastat 
                           node0           node1           node2
numa_hit                  109323          141170              77
numa_miss                      0               0               0
numa_foreign                   0               0               0
interleave_hit               519             591               0
local_node                108810          139591               0
other_node                   513            1579              77

step3: Use perf tool

root@...ntu-jammy-arm64:~/tools# perf -v
perf version 6.15.rc5.g2c3e6f60f5cf

root@...ntu-jammy-arm64:~/tools# perf list | grep -i hmu
  cxl_hmu_mem0.0.0/hotness_granual=0..0xffffffff,hotness_threshold=0..0xffffffff,downsampling_factor=0..255,.../modifier[Raw event descriptor]

root@...ntu-jammy-arm64:~/tools# perf record -a  -e cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,hotness_threshold=1024,epoperf record -a  -e cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,hotness_threshold=1024,epoch_multiplier=4,epoch_scale=4,range_base=0,range_size=1024,randomized_downsampling=0,downsampling_factor=32,hotness_granual=12/ -- sleep 10

Error:
cxl_hmu_mem0.0.0/epoch_type=0,access_type=6,hotness_threshold=1024,epoch_multiplier=4,epoch_scale=4,range_base=0,range_size=1024,randomized_downsampling=0,downsampling_factor=32,hotness_granual=12/H: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'

[1]:https://lore.kernel.org/linux-cxl/aFNsFI5OKrD0CWR3@phytium.com.cn/T/#u

Is something wrong on the CHMU interrupts?

> 
> Jonathan
> 
> > 
> > 
> > 
> > Are there any steps i am missing?
> > 
> > Regards,
> > Neeraj	 
> > 
> > >>
> > >> $perf report --dump-raw-traces
> > >>
> > >> Example output.  With a counter_width of 16 (0x10) the least significant
> > >> 4 bytes are the counter value and the unit index is bits 16-63.
> > >> Here all units are over the threshold and the indexes are 0,1,2 etc.
> > >>
> > >> . ... CXL_HMU data: size 33512 bytes
> > >> Header 0: units: 29c counter_width 10
> > >> Header 1 : deadbeef
> > >> 0000000000000283
> > >> 0000000000010364
> > >> 0000000000020366
> > >> 000000000003033c
> > >> 0000000000040343
> > >> 00000000000502ff
> > >> 000000000006030d
> > >> 000000000007031a
> > >>
> > >> Which will produce a list of hotness entries.
> > >> Bits[N-1:0] counter value
> > >> Bits[63:N] Unit ID (combine with unit size and DPA base + HDM decoder
> > >>   config to get to a Host Physical Address)
> > >>
> > >> Specific RFC questions.
> > >> - What should be in the header added to the aux buffer.
> > >>   Currently just the minimum is provided. Number of records
> > >>   and the counter width needed to decode them.
> > >> - Should we reset the counters when doing sampling "-F X"
> > >>   If the frequency is higher than the epoch we never see any hot units.
> > >>   If so, when should we reset them?
> > >>
> > >> Note testing has been light and on emulation only + as perf tool is
> > >> a pain to build on a striped back VM,  build testing has all be on
> > >> arm64 so far.  The driver loads though on both arm64 and x86 so
> > >> any problems are likely in the perf tool arch specific code
> > >> which is build tested (on wrong machine)
> > >>
> > >> The QEMU emulation needs some cleanup, but I should be able to post
> > >> that shortly to let people actually play with this.  There are lots
> > >> of open questions there on how 'right' we want the emulation to be
> > >> and what counting uarch to emulate.
> > >>
> > >> Jonathan Cameron (4):
> > >>   cxl: Register devices for CXL Hotness Monitoring Units (CHMU)
> > >>   cxl: Hotness Monitoring Unit via a Perf AUX Buffer.
> > >>   perf: Add support for CXL Hotness Monitoring Units (CHMU)
> > >>   hwtrace: Document CXL Hotness Monitoring Unit driver
> > >>
> > >>  Documentation/trace/cxl-hmu.rst     | 197 +++++++
> > >>  Documentation/trace/index.rst       |   1 +
> > >>  drivers/cxl/Kconfig                 |   6 +
> > >>  drivers/cxl/Makefile                |   3 +
> > >>  drivers/cxl/core/Makefile           |   1 +
> > >>  drivers/cxl/core/core.h             |   1 +
> > >>  drivers/cxl/core/hmu.c              |  64 ++
> > >>  drivers/cxl/core/port.c             |   2 +
> > >>  drivers/cxl/core/regs.c             |  14 +
> > >>  drivers/cxl/cxl.h                   |   5 +
> > >>  drivers/cxl/cxlpci.h                |   1 +
> > >>  drivers/cxl/hmu.c                   | 880 ++++++++++++++++++++++++++++
> > >>  drivers/cxl/hmu.h                   |  23 +
> > >>  drivers/cxl/pci.c                   |  26 +-
> > >>  tools/perf/arch/arm/util/auxtrace.c |  58 ++
> > >>  tools/perf/arch/x86/util/auxtrace.c |  76 +++
> > >>  tools/perf/util/Build               |   1 +
> > >>  tools/perf/util/auxtrace.c          |   4 +
> > >>  tools/perf/util/auxtrace.h          |   1 +
> > >>  tools/perf/util/cxl-hmu.c           | 367 ++++++++++++
> > >>  tools/perf/util/cxl-hmu.h           |  18 +
> > >>  21 files changed, 1748 insertions(+), 1 deletion(-)
> > >>  create mode 100644 Documentation/trace/cxl-hmu.rst
> > >>  create mode 100644 drivers/cxl/core/hmu.c
> > >>  create mode 100644 drivers/cxl/hmu.c
> > >>  create mode 100644 drivers/cxl/hmu.h
> > >>  create mode 100644 tools/perf/util/cxl-hmu.c
> > >>  create mode 100644 tools/perf/util/cxl-hmu.h
> > >>  
> > >  
> > 
> 

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