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Bgc suspension fixes #27729
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Bgc suspension fixes #27729
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…d_first_object when finding the start of objects for marking interior pointers.
…t in find_first_object when finding the start of objects for marking interior pointers." This reverts commit 9d53ff9.
…GC is in progress: - In background_mark_simple1, check g_fSuspensionPending and if it is set, save the state of the work and restart the loop - this will call allow_fgc() and thus allow a foreground GC to take place. - In revisit_written_page, call allow_fgc() at the end - this allow a foreground GC to happen whenever we are done with revisiting a written page.
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instead of checking something like g_fSuspensionPending, it might be better to count the already marked refs like we do with the ones we need to mark; since we do less work with marked refs we can exit the loop say 16 * num_partial_refs. this way we don't need to bring in the g_fSuspensionPending var at all (which would be more elegant 'cause it's supposed to be encapsulate in the allow_fgc logic). something like this: int num_unmarked_refs = num_partial_refs;
int num_marked_refs = num_unmarked_refs * 16;
go_through_object (method_table(oo), oo, s, ppslot,
start, use_start, (oo + s),
{
uint8_t* o = *ppslot;
Prefetch(o);
if (background_mark (o,
background_saved_lowest_address,
background_saved_highest_address))
{
// same code here
}
else if (--num_marked_refs == 0)
{
*place = (uint8_t*)(ppslot + 1);
goto more_to_do;
}
}
);what do you think? |
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I considered this but worried that the additional variable would live on the stack and thus we'd have additional memory references. I'll give it a try... |
…spensionPending directly.
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Ok, I tried your counter solution and found that the additional counter lives in a register, not on the stack (in x64 release). Also, in PerfView I could not see a speed difference between the two. I made the following small tweaks to your suggested solution:
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MichalStrehovsky
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Mar 28, 2020
* Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers. * Revert "Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers." This reverts commit dotnet/coreclr@9d53ff9. * Two fixes to speed up suspension for foreground GCs while background GC is in progress: - In background_mark_simple1, check g_fSuspensionPending and if it is set, save the state of the work and restart the loop - this will call allow_fgc() and thus allow a foreground GC to take place. - In revisit_written_page, call allow_fgc() at the end - this allow a foreground GC to happen whenever we are done with revisiting a written page. * Addressed code review feedback - use counter instead of testing g_fSuspensionPending directly. Commit migrated from dotnet/coreclr@a7678f5
MichalStrehovsky
pushed a commit
to MichalStrehovsky/corert
that referenced
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Mar 31, 2020
* Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers. * Revert "Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers." This reverts commit dotnet/coreclr@9d53ff9. * Two fixes to speed up suspension for foreground GCs while background GC is in progress: - In background_mark_simple1, check g_fSuspensionPending and if it is set, save the state of the work and restart the loop - this will call allow_fgc() and thus allow a foreground GC to take place. - In revisit_written_page, call allow_fgc() at the end - this allow a foreground GC to happen whenever we are done with revisiting a written page. * Addressed code review feedback - use counter instead of testing g_fSuspensionPending directly. Commit migrated from dotnet/coreclr@a7678f5
jkotas
pushed a commit
to dotnet/corert
that referenced
this pull request
Apr 1, 2020
* Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers. * Revert "Changes to set gen0 bricks always. This reduces the time spent in find_first_object when finding the start of objects for marking interior pointers." This reverts commit dotnet/coreclr@9d53ff9. * Two fixes to speed up suspension for foreground GCs while background GC is in progress: - In background_mark_simple1, check g_fSuspensionPending and if it is set, save the state of the work and restart the loop - this will call allow_fgc() and thus allow a foreground GC to take place. - In revisit_written_page, call allow_fgc() at the end - this allow a foreground GC to happen whenever we are done with revisiting a written page. * Addressed code review feedback - use counter instead of testing g_fSuspensionPending directly. Commit migrated from dotnet/coreclr@a7678f5
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Two fixes to speed up suspension for foreground GCs while background GC is in progress:
In background_mark_simple1, check g_fSuspensionPending and if it is set, save the state of the work and restart the loop - this will call allow_fgc() and thus allow a foreground GC to take place. Some measurements indicated this would regress performance of background_mark_simple1, but the effect seems to have disappeared when I remeasured. Nonetheless I'm curious if there is a better way.
In revisit_written_page, call allow_fgc() at the end - this allow a foreground GC to happen whenever we are done with revisiting a written page. This change was suggested by Maoni.