RFE: Graphing and iteration support for fio

Sometimes you want to run a set of experiments on a disk, varying a parameter between tests (in my case, iodepth, but buffer size is also a good candidate). You then want to present the results in a nice graph.

I wrote a small wrapper around fio to do this
(https://github.com/avikivity/diskplorer), but it occurs to me that generalized support for both in fio would be much more useful.

Possibly, you'd define a job as a template:

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
iodepth=template_variable

(it's just possible that someone can come up with better syntax).

A few more options in the global section can then cause a graph to be generated.

btw, a fast disk can easily saturate a single core using libaio, so a multithreaded libaio ioengine would be welcome (I am currently emulating it using multiple jobs and new_group).

Quoted 17 lines · Avi Kivity

Sometimes you want to run a set of experiments on a disk, varying a parameter between tests (in my case, iodepth, but buffer size is also a good candidate). You then want to present the results in a nice graph.

I wrote a small wrapper around fio to do this
(https://github.com/avikivity/diskplorer), but it occurs to me that generalized support for both in fio would be much more useful.

Possibly, you'd define a job as a template:

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
iodepth=template_variable

Quoted 4 lines

(it's just possible that someone can come up with better syntax).

A few more options in the global section can then cause a graph to be generated.

It'd be great to integrate this into fio, as graphing results is something that most people want to do. Any chance you would be willing to try and hash that out?

Quoted 4 lines

btw, a fast disk can easily saturate a single core using libaio, so a multithreaded libaio ioengine would be welcome (I am currently emulating it using multiple jobs and new_group).

In the context of fio, that doesn't make a lot of sense. A job in fio is, by definition, either a thread or a process that does IO. So if you want more threads banging on a device, then you'd add more jobs. If multiple threads shared on aio context, then we'd also potentially see contention on that part. If you just use more jobs, then each gets an aio context as well.

Quoted 20 lines · Jens Axboe

Quoted 19 lines · Avi Kivity

Sometimes you want to run a set of experiments on a disk, varying a parameter between tests (in my case, iodepth, but buffer size is also a good candidate). You then want to present the results in a nice graph.

I wrote a small wrapper around fio to do this
(https://github.com/avikivity/diskplorer), but it occurs to me that generalized support for both in fio would be much more useful.

Possibly, you'd define a job as a template:

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
iodepth=template_variable

(it's just possible that someone can come up with better syntax).

Quoted 6 lines

Quoted 2 lines

A few more options in the global section can then cause a graph to be generated.

It'd be great to integrate this into fio, as graphing results is something that most people want to do. Any chance you would be willing to try and hash that out?

I'd love to say yes, but no.

Quoted 11 lines

Quoted 3 lines

btw, a fast disk can easily saturate a single core using libaio, so a multithreaded libaio ioengine would be welcome (I am currently emulating it using multiple jobs and new_group).

In the context of fio, that doesn't make a lot of sense. A job in fio is, by definition, either a thread or a process that does IO. So if you want more threads banging on a device, then you'd add more jobs. If multiple threads shared on aio context, then we'd also potentially see contention on that part. If you just use more jobs, then each gets an aio context as well.

If your jobs are generated via a template, as above, then this is hard to do. For iodepth=1 you want one job with iodepth=1. For iodepth=64 you want 8 jobs (one per core) each with an iodepth=8; otherwise a fast SSD will overwhelm a single core.

Perhaps the job specification can be modified so that it auto-generates subjobs. In the specification, there is one entry, but fio sees 8 (or 1, when the template sets iodepth=1), and reports them via a group.

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
subjobs=(min(template_variable, core_count))
iodepth=(template_variable / subjobs)

(the above doesn't cope will with an iodepth that doesn't divide into your core_count; displorer will generate subjobs with different iodepth for this)

Quoted 23 lines · Avi Kivity

Quoted 20 lines · Jens Axboe

Quoted 19 lines · Avi Kivity

Sometimes you want to run a set of experiments on a disk, varying a parameter between tests (in my case, iodepth, but buffer size is also a good candidate). You then want to present the results in a nice graph.

I wrote a small wrapper around fio to do this
(https://github.com/avikivity/diskplorer), but it occurs to me that generalized support for both in fio would be much more useful.

Possibly, you'd define a job as a template:

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
iodepth=template_variable

(it's just possible that someone can come up with better syntax).

Quoted 8 lines

Quoted 6 lines

Quoted 2 lines

A few more options in the global section can then cause a graph to be generated.

It'd be great to integrate this into fio, as graphing results is something that most people want to do. Any chance you would be willing to try and hash that out?

I'd love to say yes, but no.

:-)

Quoted 29 lines

Quoted 11 lines

Quoted 3 lines

btw, a fast disk can easily saturate a single core using libaio, so a multithreaded libaio ioengine would be welcome (I am currently emulating it using multiple jobs and new_group).

In the context of fio, that doesn't make a lot of sense. A job in fio is, by definition, either a thread or a process that does IO. So if you want more threads banging on a device, then you'd add more jobs. If multiple threads shared on aio context, then we'd also potentially see contention on that part. If you just use more jobs, then each gets an aio context as well.

If your jobs are generated via a template, as above, then this is hard to do. For iodepth=1 you want one job with iodepth=1. For iodepth=64 you want 8 jobs (one per core) each with an iodepth=8; otherwise a fast SSD will overwhelm a single core.

Perhaps the job specification can be modified so that it auto-generates subjobs. In the specification, there is one entry, but fio sees 8 (or 1, when the template sets iodepth=1), and reports them via a group.

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
subjobs=(min(template_variable, core_count))
iodepth=(template_variable / subjobs)

Quoted 3 lines

(the above doesn't cope will with an iodepth that doesn't divide into your core_count; displorer will generate subjobs with different iodepth for this)

For purely automated or templated, yeah, it's not ideal. But some of this is highly setup specific. For QD=64, 2 threads at QD=32 might be the best option. Or 8/8, perhaps. Sometimes it's a tradeoff between throwing CPU cycles at it to squeeze out the last drop of performance, sometimes (eg on nvme), you need "just enough" threads to reach max performance, since things are mostly 100% parallelized on both the submission and completion path.

Fio does support thread offload (io_submit_mode=offload), which was added not for performance reasons, but because it's important to capture the true latency of the device in case of device backup. So the framework is in place to do that - which was the harder part. You might want to take a look at that. It would need slight modifications for your use case, but it'd be a good general addition.

Quoted 64 lines · Jens Axboe

Quoted 23 lines · Avi Kivity

Quoted 20 lines · Jens Axboe

Quoted 19 lines · Avi Kivity

Sometimes you want to run a set of experiments on a disk, varying a parameter between tests (in my case, iodepth, but buffer size is also a good candidate). You then want to present the results in a nice graph.

I wrote a small wrapper around fio to do this
(https://github.com/avikivity/diskplorer), but it occurs to me that generalized support for both in fio would be much more useful.

Possibly, you'd define a job as a template:

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
iodepth=template_variable

(it's just possible that someone can come up with better syntax).

Quoted 8 lines

Quoted 6 lines

Quoted 2 lines

A few more options in the global section can then cause a graph to be generated.

It'd be great to integrate this into fio, as graphing results is something that most people want to do. Any chance you would be willing to try and hash that out?

I'd love to say yes, but no.

:-)

Quoted 29 lines

Quoted 11 lines

Quoted 3 lines

btw, a fast disk can easily saturate a single core using libaio, so a multithreaded libaio ioengine would be welcome (I am currently emulating it using multiple jobs and new_group).

In the context of fio, that doesn't make a lot of sense. A job in fio is, by definition, either a thread or a process that does IO. So if you want more threads banging on a device, then you'd add more jobs. If multiple threads shared on aio context, then we'd also potentially see contention on that part. If you just use more jobs, then each gets an aio context as well.

If your jobs are generated via a template, as above, then this is hard to do. For iodepth=1 you want one job with iodepth=1. For iodepth=64 you want 8 jobs (one per core) each with an iodepth=8; otherwise a fast SSD will overwhelm a single core.

Perhaps the job specification can be modified so that it auto-generates subjobs. In the specification, there is one entry, but fio sees 8 (or 1, when the template sets iodepth=1), and reports them via a group.

[aio-read]
template_start=1
template_end=100
template_step=1
(or template_ratio=1.05 for exponential growth)
subjobs=(min(template_variable, core_count))
iodepth=(template_variable / subjobs)

Quoted 8 lines

Quoted 3 lines

(the above doesn't cope will with an iodepth that doesn't divide into your core_count; displorer will generate subjobs with different iodepth for this)

For purely automated or templated, yeah, it's not ideal. But some of this is highly setup specific. For QD=64, 2 threads at QD=32 might be the best option. Or 8/8, perhaps. Sometimes it's a tradeoff between throwing CPU cycles at it to squeeze out the last drop of performance, sometimes (eg on nvme), you need "just enough" threads to reach max performance, since things are mostly 100% parallelized on both the submission and completion path.

Fio does support thread offload (io_submit_mode=offload), which was added not for performance reasons, but because it's important to capture the true latency of the device in case of device backup. So the framework is in place to do that - which was the harder part. You might want to take a look at that. It would need slight modifications for your use case, but it'd be a good general addition.

Ok. For my case the existing diskplorer hack is enough, but this really belongs in fio proper.

Maybe it wants integration with a scripting language that can succinctly represent the job by returning an object (or array of objects for a multi-job test), instead of the ugly template syntax I proposed.

So you'd run 'fio test.lua' and it would generate test specifications for you, then graph them.