[lttng-dev] Question about performance and tracepoint structure
AMITM at il.ibm.com
Wed Jul 10 13:16:53 EDT 2013
This may be a bit of a noob question, and I think I read about this
somewhere but I can't find it now.
When I declare a tracepoint that's made up of a uint8_t, followed by a
uint16_t followed by a uint32_t, for example, there are 2 ways to handle
this - packed or unpacked.
If we're doing packed, then we have to include some code that does the
packing properly as alignment issues can creep up. This code causes us to
incur some CPU cycles at that point.
If we're doing unpacked, then we incur some cycles on passing the event to
the sessiond, and sessiond suffers by having to write down some extra
bytes, which is less efficient.
Either way, I think it means I can gain some minor performance
improvements if I reorder my tracepoint arguments to a more efficient
order - alignment-wise.
Am I barking up the wrong tree here?
IBM XIV - Storage Reinvented
XIV-NAS Development Team
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