Awesome, thanks Jason!
On Fri, Jun 13, 2014 at 11:51 AM, Jason Molenda <ja...@molenda.com> wrote: > The goal is that lldb won't need to ask for any additional register values > at a typical stop with the command line lldb unless the user issues > additional commands. Obviously fp, pc, sp are needed. Sometimes the > function arguments (which lldb will print with the frame format) are still > in registers -- so we include the argument registers. > > In performance tuning with iOS, we've consistently found that the size of > the packets is not particularly important - but the number of packets is > critical. I think this will be typical of remote communication with > devices where there may be several layers involved with the communication. > So it's better to include extra registers in the stop packet that lldb > might need than to have lldb ask for them individually. > > You could argue that you should just throw all of the GPRs in the stop > packet. Empirically, we've found that the sp/pc/fp/arg regs are enough and > we've never gone all the way and included all of them. Maybe with armv7 > where the gpr is relatively small in size we include them all. The smart > play is probably just to throw them all in there, even on arm64 where you > have 32 GPRs. > > A good example of the cost of packet-size vrs. number-of-packets was a > little performance tuning I did recently. We had a problem where large > memory reads from an iOS device were slow -- reading, say, 6MB of heap. I > made three changes to lldb/debugserver that got us about 12x faster reading > the same memory from a device: added a binary "x" read memory packet > (instead of ascii-hex representations of the memory, so reducing the # of > bytes sent by half), stopped adding large memory read data to lldb's memory > cache, and went from 512-byte memory reads to 128kbyte memory reads. I > didn't try to tease apart which of these were responsible for the > performance bump, but I'm willing to bet it was the increase in the size of > the memory reads and the reduction in the number of packets required. > > > > On Jun 13, 2014, at 11:18 AM, Todd Fiala <todd.fi...@gmail.com> wrote: > > > Hey Jason, > > > > Which are the registers that are most important to contain in the stop > notification expedited registers section? > > > > I'm adding tests for the ones considered essential. I right now am > checking for these generic registers: pc, sp, fp. > > > > I think you mentioned it would be nice to have some of the arg registers > as well? Anything else? > > > > The tests go upstream in llvm.org svn for debugserver, and the llgs > tests are enabled in the llgs branch and then I use that to drive the llgs > implementation. > > > > Thanks! > > -- > > -Todd > > > _______________________________________________ > lldb-dev mailing list > lldb-dev@cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev > -- Todd Fiala | Software Engineer | tfi...@google.com | 650-943-3180
_______________________________________________ lldb-dev mailing list lldb-dev@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
