Messages in this thread |  | | Date | Wed, 22 Oct 2014 10:26:25 +0200 | From | Heiko Carstens <> | Subject | Re: [PATCH v3 0/2] s390 vs. kprobes on ftrace |
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On Tue, Oct 21, 2014 at 09:58:31PM +0200, Vojtech Pavlik wrote: > Hello Heiko, > > I can confirm that kGraft works well on top of current mainline with > this patch added. > > Another reason for a performance impact when kGraft is enabled is that > kGraft still adds two instructions to the syscall path on s390x, as > there is no space left for a kgraft TIF in the first eight bits of > thread info flags. Renumbering the thread info flags such that _TIF_WORK > occupies the first eight bits and TIF_TRACE the next eight would fix > that problem: Do you believe it is feasible?
Hi Vojtech,
I think you're talking about the SLES12 kernel? There you can simply move the TIF_SYSCALL bit to the same byte where your TIF_KGR bit resides.
Upstream is a bit different since the TIF_SYSCALL bit is already gone (got replaced with an s390 specific "PIF" bit). However the free TIF bit got already eaten up by uprobes..
However we can think of a better solution for upstream if the combined solution of kGraft/kpatch is ready to be merged.
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