undefined | Better HN

0 pointsfulafel6y ago0 comments

Actual observed IPC tends to be 1 or less unless you are running well tuned computational workloads. And mostly software doesn't utilize multiple cores well.

0 comments

Veedrac6y ago

Even ‘perf stat libreoffice ./somedocument.odt’ give an IPC of almost 2, and that's hardly a well-tuned computational workload.

> And mostly software doesn't utilize multiple cores well.

Most software sucks, that's the point of this whole conversation.

fulafelOP6y ago

Valid correction, seems I was out of date, let's say 2 or below today. (I got 1.3-1.7 with a few libreoffice startup & command-line conversion experiments).

However during the boot process I think the IPC will be notably less, because there will be periods of waiting for disk IO and hardware initialization waits.

To zoom out, there are two dimensions here - it's good for software to run at a good IPC, but even better to do the job with fewer instructions.

Veedrac6y ago

Sure, I think the point of measuring CPU speed is not to say that it suffices for a fast boot, but to say that whatever it takes to boot, the CPU should not be a limiting factor.

When I think of all the things necessary to booting; discovering connected devices, loading drivers, setting up memory and permissions, loading filesystem data, starting up the graphics hardware, ... I struggle to think of many things where ‘a few milliseconds’ is not plenty of time. For sure, you might have electrical limitations, spinning disks might take multiple milliseconds, and loading dozens of megabytes of data is not instantaneous, but, really, you've got 16 whole milliseconds in a frame at 60Hz! Is that so much to ask for?

j / k navigate · click thread line to collapse

0 comments

Veedrac6y ago

Even ‘perf stat libreoffice ./somedocument.odt’ give an IPC of almost 2, and that's hardly a well-tuned computational workload.

> And mostly software doesn't utilize multiple cores well.

Most software sucks, that's the point of this whole conversation.

fulafelOP6y ago

Valid correction, seems I was out of date, let's say 2 or below today. (I got 1.3-1.7 with a few libreoffice startup & command-line conversion experiments).

However during the boot process I think the IPC will be notably less, because there will be periods of waiting for disk IO and hardware initialization waits.

To zoom out, there are two dimensions here - it's good for software to run at a good IPC, but even better to do the job with fewer instructions.

Veedrac6y ago

Sure, I think the point of measuring CPU speed is not to say that it suffices for a fast boot, but to say that whatever it takes to boot, the CPU should not be a limiting factor.

j / k navigate · click thread line to collapse