On 14.03.2013, at 05:50, Bhushan Bharat-R65777 wrote: > > >> -----Original Message----- >> From: Alexander Graf [mailto:ag...@suse.de] >> Sent: Thursday, March 07, 2013 6:56 PM >> To: Bhushan Bharat-R65777 >> Cc: kvm-...@vger.kernel.org; kvm@vger.kernel.org; Wood Scott-B07421; Bhushan >> Bharat-R65777 >> Subject: Re: [PATCH 4/7] booke: Save and restore debug registers on guest >> entry >> and exit >> >> >> On 28.02.2013, at 05:13, Bharat Bhushan wrote: >> >>> On Guest entry: if guest is wants to use the debug register then save >>> h/w debug register in host_dbg_reg and load the debug registers with >>> shadow_dbg_reg. Otherwise leave h/w debug registers as is. >> >> Why can't we switch the majority of registers on vcpu_put/get and only >> enable or >> disable debugging on guest entry/exit? > > > One of the reason for not doing this is that the KVM is a host kernel module > and let this be debugged by host (I do not this how much useful this is :)) > So I am not able to recall the specific reason, maybe we have just coded this > like this and tried to keep overhead as low as possible by switching > registers only when they are used.
My point is that the overhead is _higher_ this way, because we need to do checks and switches on every guest entry/exit, which happens a _lot_ more often than a host context switch. > As we discussed before, we can keep this option open for future. What future? Just ignore debug events in the entry/exit code path and suddenly a lot of the code becomes a lot easier. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
