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Re: Unneeded displaced single stepping causes issues: Performance drop and range stepping killer
- From: Raphael Zulliger <zulliger at indel dot ch>
- To: Tom Tromey <tromey at redhat dot com>
- Cc: gdb at sourceware dot org
- Date: Wed, 24 Apr 2013 08:58:40 +0200
- Subject: Re: Unneeded displaced single stepping causes issues: Performance drop and range stepping killer
- References: <517516D8 dot 6010604 at indel dot ch> <87li88o7fd dot fsf at fleche dot redhat dot com>
On 04/24/2013 06:53 AM, Tom Tromey wrote:
"Raphael" == Raphael Zulliger <zulliger@indel.ch> writes:
Raphael> versus:
Raphael> (gdb) set displaced-stepping 1
Raphael> (gdb) si
Raphael> Sending packet: $m1508,4#9b...Packet received: 3c000058
Raphael> Sending packet: $m832d4,4#02...Packet received: 7c0802a6
Raphael> Sending packet: $X1508,0:#bc...Packet received:
Raphael> binary downloading NOT supported by target
Raphael> Sending packet: $M1508,4:7c0802a6#b0...Packet received: OK
Raphael> Sending packet: $g#67...Packet received:
[...]
I guess this is copying the instruction and stepping it?
Yes.
I wonder if we
could put more information about displaced stepping into the remote
protocol, to avoid the extra traffic.
Good point! Something like:
vCont;d:p1.dca118
Would perfectly work for our system. (For our system it'd be required
that GDB does the displaced step fixup, as we do not (yet) support this
on the target side - others systems may even avoid that step).
Speaking in RSP, it could then look like this:
(gdb) si
Sending packet: $vCont;d:p1.dca118#83...Packet received: OK
Notification received:
Stop:T05thread:p1.dca118;0:00049cd0;1:00dcde40;2:00dca118;3:00dcdea4;4:00dcdea0;5:00000142;6:00dcde68;7:00000002;8:00000005;9:00dcdea4;a:00579e90;b:00ed4b34;c:00000000;d:f7ffffff;e:00000357;f:f1010000;10:00000000;11:fff71658;12:0068e738;13:001dd964;14:00000000;15:00000000;16:0069c120;17:00000000;18:00000037;19:00000000;1a:00000032;1b:00e6b2c0;1c:00087e48;1d:00ed12a0;1e:00ed1b68;1f:00dcde78;20:00000006347fd013;21:3ff199999999999a;22:3ff199999999999a;23:0000000000000000;24:0000000000000000;25:0000000000000000;26:0000000000000000;27:0000000000000000;28:0000000000000000;29:0000000000000000;2a:0000000000000000;2b:0000000000000000;2c:401900a3d70a3d71;2d:3ff199999999999a;2e:0000000000000000;2f:0000000000000000;30:0000000000000000;31:0000000000000000;32:0000000000000000;33:0000000000000000;34:0000000000000000;35:0000000000000000;36:0000000000000000;37:0000000000000000;38:0000000000000000;39:0000000000000000;3a:0000000000000000;3b:0000000000000000;3c:0000000000000000;3d:0000000000000000;3e:0000000000000000;3f:0000000000000000;46:efbeadde;40:0000150c;41:0008a030;42:20000004;43:00049cd0;44:00000000;45:00000000;
Sending packet: $vStopped#55...Packet received: OK
Sending packet: $P40=000832d8#ba...Packet received: OK
vs:
(gdb) si
Sending packet: $m1508,4#9b...Packet received: 3c000058
Sending packet: $m832d4,4#02...Packet received: 7c0802a6
Sending packet: $M1508,4:7c0802a6#b0...Packet received: OK
Sending packet: $g#67...Packet received:
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
Sending packet: $P40=00001508#7f...Packet received: OK
Sending packet: $vCont;s:p1.dca118#83...Packet received: OK
Notification received:
Stop:T05thread:p1.dca118;0:00049cd0;1:00dcde40;2:00dca118;3:00dcdea4;4:00dcdea0;5:00000142;6:00dcde68;7:00000002;8:00000005;9:00dcdea4;a:00579e90;b:00ed4b34;c:00000000;d:f7ffffff;e:00000357;f:f1010000;10:00000000;11:fff71658;12:0068e738;13:001dd964;14:00000000;15:00000000;16:0069c120;17:00000000;18:00000037;19:00000000;1a:00000032;1b:00e6b2c0;1c:00087e48;1d:00ed12a0;1e:00ed1b68;1f:00dcde78;20:00000006347fd013;21:3ff199999999999a;22:3ff199999999999a;23:0000000000000000;24:0000000000000000;25:0000000000000000;26:0000000000000000;27:0000000000000000;28:0000000000000000;29:0000000000000000;2a:0000000000000000;2b:0000000000000000;2c:401900a3d70a3d71;2d:3ff199999999999a;2e:0000000000000000;2f:0000000000000000;30:0000000000000000;31:0000000000000000;32:0000000000000000;33:0000000000000000;34:0000000000000000;35:0000000000000000;36:0000000000000000;37:0000000000000000;38:0000000000000000;39:0000000000000000;3a:0000000000000000;3b:0000000000000000;3c:0000000000000000;3d:0000000000000000;3e:0000000000000000;3f:0000000000000000;46:efbeadde;40:0000150c;41:0008a030;42:20000004;43:00049cd0;44:00000000;45:00000000;
Sending packet: $vStopped#55...Packet received: OK
Sending packet: $M1508,4:3c000058#78...Packet received: OK
Sending packet: $P40=000832d8#ba...Packet received: OK
That would be quite an improvement!
While we are at it... I've got another note related to single-stepping:
For our system, once a 'vCont;s:' returns with "OK", the single-step has
already been performed. Maybe this is also the case for the majority of
the systems out there? For systems like ours, we could get rid of the
stop notification, by returning the content of the stop reply (sig
number & registers) right in the vCont reply. (And, of course, the same
would be true for range stepping.) That would again reduce the
communication to something like:
(gdb) si
Sending packet: $vCont;d:p1.dca118#83...Packet received:
T05thread:p1.dca118;0:00049cd0;1:00dcde40;2:00dca118;3:00dcdea4;4:00dcdea0;5:00000142;6:00dcde68;7:00000002;8:00000005;9:00dcdea4;a:00579e90;b:00ed4b34;c:00000000;d:f7ffffff;e:00000357;f:f1010000;10:00000000;11:fff71658;12:0068e738;13:001dd964;14:00000000;15:00000000;16:0069c120;17:00000000;18:00000037;19:00000000;1a:00000032;1b:00e6b2c0;1c:00087e48;1d:00ed12a0;1e:00ed1b68;1f:00dcde78;20:00000006347fd013;21:3ff199999999999a;22:3ff199999999999a;23:0000000000000000;24:0000000000000000;25:0000000000000000;26:0000000000000000;27:0000000000000000;28:0000000000000000;29:0000000000000000;2a:0000000000000000;2b:0000000000000000;2c:401900a3d70a3d71;2d:3ff199999999999a;2e:0000000000000000;2f:0000000000000000;30:0000000000000000;31:0000000000000000;32:0000000000000000;33:0000000000000000;34:0000000000000000;35:0000000000000000;36:0000000000000000;37:0000000000000000;38:0000000000000000;39:0000000000000000;3a:0000000000000000;3b:0000000000000000;3c:0000000000000000;3d:0000000000000000;3e:0000000000000000;3f:0000000000000000;46:efbeadde;40:0000150c;41:0008a030;42:20000004;43:00049cd0;44:00000000;45:00000000;
Sending packet: $P40=000832d8#ba...Packet received: OK
Tom