Message 148595 - Python tracker

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Author	vstinner
Recipients	gvanrossum, jpe, loewis, pitrou, rhettinger, sdeibel, vstinner
Date	2011-11-29.19:11:31
SpamBayes Score	5.8162554e-05
Marked as misclassified	No
Message-id	<1322593892.27.0.977834287136.issue5654@psf.upfronthosting.co.za>
In-reply-to

Content
> the cost in the normal case is a single pointer comparison with NULL, > something very cheap. The Linux kernel patchs dynamically the code: disabling a probe writes NOP instruction in memory to avoid the cost of the test. Probes are completly disabled by default. See kernel markers (introduced in Linux 2.6.24) and the more recent kernel tracepoints (introduced in Linux 2.6.28). http://lwn.net/Articles/300992/ > If something like this goes in, it should be #ifdef'd out > by default I agree.

> the cost in the normal case is a single pointer comparison with NULL,
> something very cheap.

The Linux kernel patchs dynamically the code: disabling a probe writes NOP instruction in memory to avoid the cost of the test. Probes are completly disabled by default.

See kernel markers (introduced in Linux 2.6.24) and the more recent kernel tracepoints (introduced in Linux 2.6.28).
http://lwn.net/Articles/300992/

> If something like this goes in, it should be #ifdef'd out
> by default

I agree.

History
Date	User	Action	Args
2011-11-29 19:11:32	vstinner	set	recipients: + vstinner, gvanrossum, loewis, rhettinger, jpe, sdeibel, pitrou
2011-11-29 19:11:32	vstinner	set	messageid: <1322593892.27.0.977834287136.issue5654@psf.upfronthosting.co.za>
2011-11-29 19:11:31	vstinner	link	issue5654 messages
2011-11-29 19:11:31	vstinner	create