| Title | MPS gc-start and -end messages give no idea of timing |
| Status | closed |
| Priority | essential |
| Assigned user | Richard Kistruck |
| Organization | Ravenbrook |
| Description | MPS gc-start and -end messages give no idea of timing. Summary: mps_message_clock() -- new function in mps.h Related jobs: job001968: "MPS clients get no synchronous alert of collection begin/end" RHSK 2008-11-12 The messages are asynchronous (and therefore have no implicit timestamp), and they have no explicit timestamp. |
| Analysis | RHSK 2008-11-12 Give gc-start and -end messages an explicit timestamp as they are posted with MessagePost(). Use the mps_clock() plinth facility (see mpslib.h). Client accesses timestamp with new accessor mps_message_clock(). Note: gc messages are not very numerous, so calling mps_clock as they are posted is fine. Whereas finalization messages might be extremely numerous (although I have no numbers to hand), and would not benefit from timestamps -- there is nothing very useful about the time the MPS happens to discovers that an object is finalizable. Therefore, to avoid risk of performance regression due to excessive library calls to mps_clock(), do not set the timestamp on finalization messages. __Implementation__ MPS uses two sorts of time values: mps_clock_t: a plinth-supplied arithmetic type, with values >= 0, modelled on ISO C time.h's clock(). mps_clock()'s return value signifies absolute CPU time since process start. We also use mps_clock_t for relative clock values. Convert to/from seconds with factor mps_clocks_per_sec(). double (seconds): time interval in seconds (including fractions of a second). mps_clock_t is sometimes stored in and treated as a Word (both have underlying type "unsigned long" in C on all platforms, currently). This is rather a mess, so clear it up: new internal type Clock; new wrappers for mps_clock and mps_clocks_per_sec. (optional) new internal type Timespan, with TimespanClock() and ClockTimespan() converters; call mps_clocks_per_sec once in ArenaInit and store the result in ArenaStruct to avoid calling mps_clocks_per_sec() all over the place! RHSK 2008-11-12 Concern: I added the postedClock field to MessageStruct, so it imposes a memory cost for finalization messages that never use the field, which means a additional memory cost for every object for which the client calls mps_finalize. This memory cost is a regression. It could be cured by making mps_message_clock() dispatch on message type. Methods for gc-start and -end messages would use storage specific to those message types. RHSK 2008-11-24 Fix concern: regain previous small size by moving "MessageType type" field from MessageStruct to MessageClassStruct. This also usefully simplifies the relationship between message types and message classes. |
| How found | unknown |
| Evidence | none |
| Observed in | 1.108.2 |
| Created by | Richard Kistruck |
| Created on | 2008-11-12 15:35:51 |
| Last modified by | Gareth Rees |
| Last modified on | 2010-10-06 22:15:39 |
| History | 2008-11-12 RHSK Created. 2008-11-12 RHSK Concern: the current implementation has added a additional memory cost to finalized objects. 2008-11-24 RHSK Fix concern: regain previous small size. 2009-02-17 RHSK (update name of related job001968) |
| Change | Effect | Date | User | Description |
|---|---|---|---|---|
| 166809 | closed | 2008-11-25 12:56:15 | Richard Kistruck | MPS br/timing: RefMan: add entry for mps_message_clock() |
| 166796 | closed | 2008-11-24 16:20:35 | Richard Kistruck | MPS br/timing: design/message: Write new .class.type: each class now implements exactly one type. .class.not-type is now false; mark it as obsolete. |
| 166795 | closed | 2008-11-24 15:44:27 | Richard Kistruck | MPS br/timing: move field "MessageType type" out of MessageStruct and into MessageClassStruct. |
| 166702 | closed | 2008-11-12 10:02:52 | Richard Kistruck | MPS br/timing: MessageClocked(), used in MessageCheck and to prevent numerous messages (namely: finalization messages) being timestamped. |
| 166701 | open | 2008-11-12 09:26:48 | Richard Kistruck | MPS br/timing: new ClockNow() wrapper for mps_clock(), ClocksPerSec(); use Clock in arena step (not Word). |
| 166697 | open | 2008-11-11 16:57:30 | Richard Kistruck | MPS br/timing: new type "Clock", internal equivalent of mps_clock_t. Used for a field in messages. (More uses to follow). |
| 166696 | open | 2008-11-11 16:22:26 | Richard Kistruck | MPS br/timing: mpsi_check(): Check that external and internal messsage types match. |
| 166695 | open | 2008-11-11 15:28:28 | Richard Kistruck | MPS br/timing: finalcv.c: verify that message clock is 0 (unset) for finalization messages. |
| 166690 | open | 2008-11-11 10:39:53 | Richard Kistruck | MPS br/timing: Do not set postedClock for finalization msgs. |
| 166689 | open | 2008-11-11 10:31:48 | Richard Kistruck | MPS br/timing: amcss output changes: - Keep counts of both collection start messages and collection end messages. Upon receipt of these messages, format the collection start/end reports as 'brackets' (makes it easier to see whether allocation continues during the collection or not). - If mps_collections has changed, report() messages before doing anything else. - (source code clarity) Guess that the naked "4" in the mps_arena_has_addr test means "hitsWanted", and label it. |
| 166677 | open | 2008-11-07 16:11:37 | Richard Kistruck | MPS br/timing: message.c: maintain postedClock field, set it with mps_clock() at post time; amcss.c: call and display mps_message_clock() on _gc_start & _gc messages. |
| 166676 | open | 2008-11-07 15:22:24 | Richard Kistruck | MPS br/timing: (cosmetic) re-format report()'s switch on message type to comply with design/cstyle. |