move all projects into the trunk directory

[lttv.git] / ltt / tags / LinuxTraceToolkitViewer-0.10.0-pre-115102007 / doc / developer / lttng-xen.txt

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-
-
-LTTng for Xen
-
-Design document
-
-Mathieu Desnoyers, November 2006
-
-Last modification :
-
-Only allow a single channel. Directory consumed by a lttd-xen client through
-hypercalls. This design choice is made because there are no RCU lists and there
-is no link between the number of CPUs seen by Xen and number of CPUs in the
-dom0.
-
-Does better than Xentrace :
-Variable size records
-Easily extensible event description
-// not planned : missing RCU list. Multiple active traces
-Reader uses poll()-like mechanism instead of polling the buffers each 100ms.
-
-
-* Dom0 lttd-xen process
-
-Does an hypercall to map the buffers (increment refcount)
-Does an hypercall to poll for data, put to sleep by the OS.
-Uses write from the mapped buffers to a file.
-unmap buffer, decrement refcount.
-
-
-* Xen
-
-tb_control (hypercalls seen from dom0 OS)
-(hypercalls done by lttctl-xen)
-- trace_create
-Map a page for control information, return it for mapping by user space. (rw)
-Map multiple pages for buffers. return them for mapping by user space.
-(shared, read-only for consumer)
-increment refcount
-- trace_start
-Activate tracing in control information.
-- trace_stop
-Stop tracing in control information.
-- trace_destroy
-wait for pending writers (is the hypervisor preemptible ? not full.)
-  Preemption : not full -> spinlock does not disable preemption : would deadlock
-  for the non irq_disable case.
-  volountary : poll call -> volountary. explicit __schedule call., do_yield().
-Quiescent state detection.
-  for_each_domain( d )
-    for_each_vcpu( d, v )
-      vcpu_sleep_sync(v);
-decrement refcount : destroy the channels
-
-Events coming from xen :
-- Buffer switch
-  through virq sent to dom0
-- wakes up poll on the buffers FD.
-
-
-* Dom0 Linux OS
-
-Receive virq upon buffer switch.
-xen_wakeup_readers handler : wakes up the readers for the channel.
-
-Hypercalls are autonomous from LTTng linux kernel tracing.
-
-on lttngxentrace create, hypercall channel_create
-on lttngxentrace start, hypercall channel_start
-on lttngxentrace stop, hypercall channel_stop
-on lttngxentrace destroy, hypercall channel_destroy
-
-
-* Facilities
-
-Export a facilities per cpu channel too.
-
-
-Q1 : In Xen preemptible ? Full ? Volountary ? Volountary X
-Q2 : How to synchronize to wait for writers to finish writing ? X
-
-
-Number of CPUs in dom0 != number of CPUs in Xen.
-CPU hotplug in kernel tracing ? Done.
-
-