Messages in this thread | | | Date | Wed, 26 Sep 2012 16:07:34 +0900 | Subject | Re: [QUESTION] Can uprobe_event support @ADDR, $retval, offs(FETCHARG)? | From | Hyeoncheol Lee <> |
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2012/9/26 Srikar Dronamraju <srikar@linux.vnet.ibm.com>: >> >> Perhaps, it is not so small things, but at least, we can try. >> In the userspace, memories(pages) can be paged out on swap or >> files. In that case, memory dereference function needs to track >> down the data on the disk and it causes I/O. This means we will >> see the visible performance degradation with tracing. >> And also, sometime a pointer value (address) is broken, in that >> case we have to ensure the address is actually valid before >> accessing it. >> >> Of cause, without tracking paged-out data, it is easy >> to support, because that is already done in kprobe event. >> I'm not sure how it is useful, because sometimes it will >> fail to access gather the data. >> However it is good for the first step, I think. >> >> Srikar, what would you think? > > I think we should do the best effort basis first. i.e support for > tracking data thats not paged out. > Most times the data that is requested tends to the hot data. > > We could look at supporting data that is paged out later. > >> >> BTW, if we can support offs(FETCHARGS), $stack and $stackN >> are also available. ;) >> > > -- > Thanks and Regards > Srikar Dronamraju >
I asked this question. because I need Perf that supports to access user process's variables. and I am trying to add this feature.
Thank you for your answer.
Hyeoncheol
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