On 12/12/2024 12:03 pm, Mike Leach wrote:
Hi James
On Tue, 3 Dec 2024 at 14:25, James Clark james.clark@linaro.org wrote:
On 27/11/2024 1:42 pm, Mike Leach wrote:
Add an example config table generator to test loading configuration tables.
Provides a table buffer writer function that can be re-used in other userspace programs.
Table write format matches that expected by the corresponding reader in the configfs driver code.
Generates tables and outputs in form of binary files.
Add a config table file reader and printer. Takes in config table files and prints the contents. Uses table reader source from kernel driver.
Signed-off-by: Mike Leach mike.leach@linaro.org
MAINTAINERS | 1 + .../coresight/coresight-config-table.h | 5 +
Hi Mike,
Isn't there some convention about maintaining a copy of kernel headers in the tools? Especially as you wouldn't rebuild the tools after updating the kernel headers so breakages might go unnoticed.
Not sure - perf keeps a copy and has a check script on build to ensure the copy matches the kernel version. Keeping two copies of the same thing always strikes me as poor practice, so I went for copying over.
Both methods risk breakages when something in the kernel changes.
You might want to check tools/include/uapi/README which goes over it in more detail. I don't think it claims that it's perfect, but just better than alternatives. It would make sense to follow it for consistency more than anything.
[...]
+/*
- sets of presets leaves strobing window constant while varying period to allow
- experimentation with mark / space ratios for various workloads
- */
+static u64 afdo_set_a_presets[AFDO_NR_PRESETS][AFDO_NR_PARAM_SUM] = {
{ 2000, 100 },{ 2000, 1000 },{ 2000, 5000 },{ 2000, 10000 },{ 4000, 100 },The comment above here looks like its for example1, this one does vary the window size.
Probably only example2 is enough, I assumed they were different but example2 is basically the same as example1 with an extra preset list. We could comment that the second preset list is optional and delete example1. Saves people reading more and wondering what the difference is.
Yes - perhaps both examples were not necessary - but the point was you can have two configs in a single loadable table.
I tried to make an example that doesn't use an existing feature by reacreating afdo from scratch which I thought would be a good example. It's pasted at the end. I had to copy paste the ETMv4 macros and constants though, I couldn't include them in the userspace generator because of this error:
The updated ETM config set that is to follow addresses this issue - the macros are split off into a separate file (and adds in a whole lot of validation - ensuring a configuration cannot specify and allocate more resources than are available.) This is also the reason that the examples provided were very simple. More complex ones are to follow!
This set was focused on loading tables so that the next patchsets dealing with resource validating ETM configs and CTI configs had an easy to use test platform.
coresight-config.h:10:10: fatal error: linux/coresight.h: No suchfile or directory 10 | #include <linux/coresight.h>
I also got this error when loading it:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
cscfg_reset_feat (drivers/hwtracing/coresight/coresight-config.c:64 coresight-config.c:124) coresight cscfg_load_config_sets (drivers/hwtracing/coresight/coresight-syscfg.c:217 coresight-syscfg.c:262 coresight-syscfg.c:492 coresight-syscfg.c:610) coresight cscfg_dyn_load_cfg_table (drivers/hwtracing/coresight/coresight-syscfg-configfs.c:294) coresight cscfg_cfg_load_table_write (drivers/hwtracing/coresight/coresight-syscfg-configfs.c:799) coresight configfs_release_bin_file (fs/configfs/file.c:415) __fput (fs/file_table.c:432) __fput_sync (fs/file_table.c:517) __arm64_sys_close (fs/open.c:1568 fs/open.c:1550 fs/open.c:1550) invoke_syscall (arch/arm64/kernel/syscall.c:? arch/arm64/kernel/syscall.c:49) el0_svc_common (include/linux/thread_info.h:127 arch/arm64/kernel/syscall.c:140) do_el0_svc (arch/arm64/kernel/syscall.c:152)
I'll go back to my tests to check I was testing what I thought I was - and didn't accidentally change something after testing and before sending the patchset.
So I'm wondering if we can do the same thing by setting values via individual files rather than one binary blob which would avoid some of these issues. From what I understand the feature params can already be set directly this way via /sys/kernel/config/cs-syscfg/features/strobing/params/period/value
We'd have to add a way to add new configs with a mkdir, then the same things can be configured without needing an additional tool. Links between features and configs can be done with symlinks which is also mentioned in the configfs docs.
Something like this would be a bit like the current version:
# ls /config/cs-syscfg configurations features
# mkdir /config/cs-syscfg/features/my_config # ls /config/cs-syscfg/features/my_config description matches regs_desc params
# mkdir /config/cs-syscfg/features/my_config/regs_desc/TRCRSCTLRn0 # ls /config/cs-syscfg/features/my_config/TRCRSCTLRn0 type offset val mask
This is precisely what I wanted to avoid. Doing it this way is both time consuming for the user and ends up reproducing most of the sysfs files in configfs.
I thought I'd suggest the alternative in case Christoph's previous comment about not loading a binary blob was a hard nack. I understand your counter points about why the blob is better automatically, but I don't think any of them are completely unsolvable or blocking with the alternate implementation.
For the point about being time consuming, personally I found it quite time consuming to use the compiler and write in C. Rather than a pasted bash script that just lists each config element:
echo "12" > /config/cs-syscfg/features/my_config/TRCRSCTLRn0 echo "11" > /config/cs-syscfg/features/my_config/TRCRSCTLRn1 ... etc ...
Parameters are there to allow a limited amount of relevent runtime adjustment. Parameter values may also only populate part of a hw register depending on use case.
The resource approach allows us to define certain bitfields e.g.>
Branch broadcast - as user configurable - but omit anything users are
not allowed to meddle with.
This sounds like a mask file along side each register could be used to determine which bits to populate for a specific use case. And there could be kernel and user provided masks to limit which bits are written.
The table load is atomic - it is validated and succeeds or fails completely. The load mechanism prevents the new configuration from becoming visible until it is loaded. The configfs per file method has an issue in deciding when the configuration is "complete". If you look in the configfs docs/source there was at one time a "commit" methodology proposed, but this never came to fruition.
Yeah I was going to suggest some kind of "commit" file or "active" flag. Or by creating a symlink into an "active" folder at which point the config becomes write only (or writes are cached until the next use of the config which Suzuki suggested for another sysfs change on the list at the moment).
For validation, each field would be validated on write whether the config is already active or not. So presumably a script writing a list of config values would fail before reaching the "activation" or "commit" step.
Table load re-uses the same mechanisms as the built-in and loadable module methods for adding configurations, but without the need for re-compiling the kernel / compiling against a specific kernel - meaning loadable tables are dependent only on the hardware available, not the kernel version.
Isn't this the same as with the file approach? Even with the binary blob you can't configure a device that the kernel doesn't know about. And plain text files can be written to and reconfigured without recompiling or using a specific kernel version.
Adding a per file option means that the new configurations would be different from the current load methods upstream
This is true, but this binary blob compiler also felt quite different, and I wasn't able to blindly copy paste the existing autofdo config into it. It needed just as much work to get it to compile as it would have been to write the equivalent bash script echoing the config values.
- and appear differently in configfs.
I don't think that my suggestion requires that it appears differently at the point of use though. After a successful activation the configs could appear for use in the same way as the existing module loaded configs.
With all of that said both mechanisms accomplish the same thing, so I can't really say to definitely not to it the binary way. Just that it feels a bit unusual. Apart from the ACPI example, which is more of a firmware thing than something that's controlled by a user at runtime, I'm not sure if there is an example of a configfs interface like this?
James
But another way could be to enumerate all possible regs for each device. This would remove the need to have all the #defines in whatever tool is making the config (avoiding the #include issue from above):
# mkdir /config/cs-syscfg/features/my_config # ls /config/cs-syscfg/features/my_config/regs_desc
regs_desc is initially empty, but specify what device it's for to make all the properties appear (or the mkdir could be done in an etmv4 folder):
# echo "SRC_ETM4" > matches # ls /config/cs-syscfg/features/my_config/regs_desc TRCRSCTLRn0 TRCRSCTLRn1 TRCRSCTLRn2 ... etc ...
Now type and offset don't need to be set:
# ls /config/cs-syscfg/features/my_config/regs_desc/TRCRSCTLRn0 val mask save
Don't we already have the full list of parameters in etm4_cfg_map_reg_offset(), so we can expose this to users via configfs directly rather than needing any tooling. And doesn't any new device that's supported by the config mechanism need to know about all its parameters, so it wouldn't remove any flexibility?
Mike
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK