On 22.06.2020 18:02, Michał Leszczyński wrote: > ----- 22 cze 2020 o 17:22, Jan Beulich jbeul...@suse.com napisał(a): >> On 22.06.2020 16:35, Michał Leszczyński wrote: >>> ----- 22 cze 2020 o 15:25, Jan Beulich jbeul...@suse.com napisał(a): >>>> Is any of what you do in this switch() actually legitimate without >>>> hvm_set_vmtrace_pt_size() having got called for the guest? From >>>> remarks elsewhere I imply you expect the param that you currently >>>> use to be set upon domain creation time, but at the very least the >>>> potentially big buffer should imo not get allocated up front, but >>>> only when tracing is to actually be enabled. >>> >>> Wait... so you want to allocate these buffers in runtime? >>> Previously we were talking that there is too much runtime logic >>> and these enable/disable hypercalls should be stripped to absolute >>> minimum. >> >> Basic arrangements can be made at domain creation time. I don't >> think though that it would be a good use of memory if you >> allocated perhaps many gigabytes of memory just for possibly >> wanting to enable tracing on a guest. >> > > From our previous conversations I thought that you want to have > as much logic moved to the domain creation as possible. > > Thus, a parameter "vmtrace_pt_size" was introduced. By default it's > zero (= disabled), if you set it to a non-zero value, then trace buffers > of given size will be allocated for the domain and you have possibility > to use ipt_enable/ipt_disable at any moment. > > This way the runtime logic is as thin as possible. I assume user knows > in advance whether he/she would want to use external monitoring with IPT > or not.
Andrew - I think you requested movement to domain_create(). Could you clarify if indeed you mean to also allocate the big buffers this early? > It's also not "many gigabytes". In most use cases a buffer of 16/32/64 MB > would suffice, I think. But that one such buffer per vCPU, isn't it? Plus these buffers need to be physically contiguous, which is an additional possibly severe constraint. Jan
