On Fri, Jul 17, 2015 at 04:34:09PM +0300, Alexander Shishkin wrote: > Currently, the PT driver zeroes out the status register every time before > starting the event. However, all the writable bits are already taken care > of in pt_handle_status() function, except the new PacketByteCnt field, > which in new versions of PT contains the number of packet bytes written > since the last sync (PSB) packet. Zeroing it out before enabling PT forces > a sync packet to be written. This means that, with the existing code, a > sync packet (PSB and PSBEND, 18 bytes in total) will be generated every > time a PT event is scheduled in. > > To avoid these unnecessary syncs and save a WRMSR in the fast path, this > patch adds a new attribute config bit "no_force_psb", which will disable > this zeroing WRMSR.
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