Fix missing co-fixed-read and co-fixed-write tags in mixed mode HDR histograms

[Copilot]

Problem Fixed

The mixed mode was missing "co-fixed-read" and "co-fixed-write" tags in HDR histogram output because the DoMixed function wasn't calling RecordReadCoFixedLatency and RecordWriteCoFixedLatency methods.

Solution

Modified DoMixed function in modes.go to calculate and record coordinated omission fixed latency for both read and write operations by:

1. Retrieving expectedStartTime from rateLimiter.Expected() within the test function
2. Calling RecordWriteCoFixedLatency after successful write operations
3. Calling RecordReadCoFixedLatency after successful read operations
4. Calculating co-fixed latency as endTime.Sub(expectedStartTime)

This ensures HDR histogram files now include all expected tags: raw, co-fixed, raw-read, co-fixed-read, raw-write, co-fixed-write.

Changes Made

• modes.go: Fixed mixed mode coordinated omission fixed latency recording
• modes_test.go: Added test for mixed mode latency recording logic

Testing

• ✅ All existing tests continue to pass
• ✅ New test validates coordinated omission calculation logic
• ✅ Build process completes successfully
• ✅ Mixed mode now properly records both raw and coordinated omission fixed latency for read and write operations

The changes are minimal and focused, affecting only the mixed mode latency recording without altering any other functionality.

Original prompt

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This section details on the original issue you should resolve

<issue_title>New added "mixed" load: results has no "co-fixed-read" and "co-fixed-write" tags</issue_title>
<issue_description>After merging of #211
I created local scylla-bench image on top of "master", as:

DOCKER_IMAGE_TAG=mixed_load make build-docker-image

And ran mixed load with command below and saved HDR results in the file:

docker run -it -v /home/juliayakovlev/Downloads:/home --rm --network=host mixed_load -workload uniform -mode mixed -nodes 127.0.0.1 -concurrency 64 -duration 300s --hdr-latency-file=/home/hdrh-scyllabench-mixed.hdr

This is the result file:
hdrh-scyllabench-mixed.hdr.log

The flags in the results file are:

• co-fixed
• raw
• raw-read
• raw-write

I did not find tags "co-fixed-read" and "co-fixed-write".

And what is the difference between "raw" and "co-fixed"?</issue_description>

<agent_instructions>check why some of the tags are missing from the PR recently merged</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #214

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[fruch]

@CodeLieutenant can you follow @copilot into fixing this one ? and let @juliayakovlev try it to confirm it's working as expected

[juliayakovlev]

@CodeLieutenant can you follow @copilot into fixing this one ? and let @juliayakovlev try it to confirm it's working as expected

I re-run the test with new created docker image.
hdrh-scyllabench-mixed.hdr.log

Missed co-fixed-write and co-fixed-read tags are found.
But there are 2 questions:

• New added "mixed" load: results has no "co-fixed-read" and "co-fixed-write" tags #214 (comment)
• New added "mixed" load: results has no "co-fixed-read" and "co-fixed-write" tags #214 (comment)