From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Vojtech Pavlik <vojtech@suse.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
Ingo Molnar <mingo@redhat.com>, Jiri Kosina <jkosina@suse.cz>,
Jiri Slaby <jslaby@suse.cz>, Steven Rostedt <rostedt@goodmis.org>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 0/2] s390 vs. kprobes on ftrace
Date: Wed, 22 Oct 2014 10:26:25 +0200 [thread overview]
Message-ID: <20141022082625.GB4090@osiris> (raw)
In-Reply-To: <20141021195831.GA31587@suse.cz>
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.
next prev parent reply other threads:[~2014-10-22 8:26 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-21 8:30 [PATCH v3 0/2] s390 vs. kprobes on ftrace Heiko Carstens
2014-10-21 8:30 ` [PATCH v3 1/2] kprobes: introduce weak arch_check_ftrace_location() helper function Heiko Carstens
2014-10-21 9:30 ` Masami Hiramatsu
2014-10-21 12:00 ` Heiko Carstens
2014-10-21 12:11 ` Masami Hiramatsu
2014-10-21 13:16 ` Steven Rostedt
2014-10-21 8:30 ` [PATCH v3 2/2] s390/ftrace,kprobes: allow to patch first instruction Heiko Carstens
2014-10-21 19:58 ` [PATCH v3 0/2] s390 vs. kprobes on ftrace Vojtech Pavlik
2014-10-22 8:26 ` Heiko Carstens [this message]
2014-10-22 9:37 ` Vojtech Pavlik
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