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801bb689ca
Add debug.sizeof.g_stat sysctl.
Set the id field of the g_stat when we create consumers and providers.
Remove biocount from consumer, we will use the counters in the g_stat
structure instead. Replace one field which will need to be atomically
manipulated with two fields which will not (stat.nop and stat.nend).
Change add companion field to bio_children: bio_inbed for the exact
same reason.
Don't output the biocount in the confdot output.
Fix KASSERT in g_io_request().
Add sysctl kern.geom.collectstats defaulting to off.
Collect the following raw statistics conditioned on this sysctl:
for each consumer and provider {
total number of operations started.
total number of operations completed.
time last operation completed.
sum of idle-time.
for each of BIO_READ, BIO_WRITE and BIO_DELETE {
number of operations completed.
number of bytes completed.
number of ENOMEM errors.
number of other errors.
sum of transaction time.
}
}
API for getting hold of these statistics data not included yet.
41 lines
1.8 KiB
Plaintext
41 lines
1.8 KiB
Plaintext
$FreeBSD$
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For the lack of a better place to put them, this file will contain
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notes on some of the more intricate details of geom.
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-----------------------------------------------------------------------
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Locking of bio_children and bio_inbed
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bio_children is used by g_std_done() and g_clone_bio() to keep track
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of children cloned off a request. g_clone_bio will increment the
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bio_children counter for each time it is called and g_std_done will
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increment bio_inbed for every call, and if the two counters are
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equal, call g_io_deliver() on the parent bio.
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The general assumption is that g_clone_bio() is called only in
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the g_down thread, and g_std_done() only in the g_up thread and
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therefore the two fields do not generally need locking. These
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restrictions are not enforced by the code, but only with great
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care should they be violated.
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It is the responsibility of the class implementation to avoid the
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following race condition: A class intend to split a bio in two
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children. It clones the bio, and requests I/O on the child.
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This I/O operation completes before the second child is cloned
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and g_std_done() sees the counters both equal 1 and finishes off
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the bio.
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There is no race present in the common case where the bio is split
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in multiple parts in the class start method and the I/O is requested
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on another GEOM class below: There is only one g_down thread and
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the class below will not get its start method run until we return
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from our start method, and consequently the I/O cannot complete
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prematurely.
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In all other cases, this race needs to be mitigated, for instance
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by cloning all children before I/O is request on any of them.
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Notice that cloning an "extra" child and calling g_std_done() on
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it directly opens another race since the assumption is that
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g_std_done() only is called in the g_up thread.
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