From mboxrd@z Thu Jan 1 00:00:00 1970 From: Francois Wellenreiter Date: Wed, 11 May 2005 06:06:54 +0000 Subject: Re: KDB improvements for IA64 Message-Id: <4281A0FE.1030300@bull.net> List-Id: References: <4280D2C5.3060604@bull.net> In-Reply-To: <4280D2C5.3060604@bull.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>>>On Tue, 10 May 2005 17:27:01 +0200, Francois Wellenreiter said: > > > Francois> - timeouts when exiting from KDB will never occur I have > Francois> noticed that after a long time in KDB, some drivers enter > Francois> in timeout sequences. Now, the different ITC values are > Francois> saved when entering KDB and restored when going out. > > This sounds fragile to me. For one thing, the kernel may not use ITC > at all for timeouts (true for most NUMA platforms). Also, even if the > ITC is in use, you'd probably have to resync them on the slave CPUs > after restoring the time-keeper's ITC value. Not to mention that if > the timeout is related to an external event, then faking time won't > help no matter what. > > --david > - > To unsubscribe from this list: send the line "unsubscribe linux-ia64" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > David, I agree that ITC management may be a bit risky and overall is platform-dependent, but in my opinion, that was a better way than saving and restoring global xtime variable which can be modified by only one CPU (the main danger in such a case may occur when this CPU is working when the other ones are already running KDB). The time-outs that I have noticed dealt with journalled filesystem messages (and sometimes lead to an unrecoverable machine crash), that is the reason why I have implemented this feature. On the different NUMA machines that I have tested, this problem did not appear again. If you have some implementation ideas, they are really welcome. Regards, Francois