Measure Reference Manual

Measure and the ALL_OPENS resource limit in the OSS SCF interface represent the same
value.)
For more information on OSS environmental limits, see the Open System Services Management
and Operations Guide.
• A read or write operation on a regular file can be sent directly to DP2 or satisfied via the OSS
file system cache.
◦ Noncached operations (FS-DIRECT-READS, FS-DIRECT-WRITES) result in messages to DP2
and transfer only as much information as specified by the client.
◦ Cached operations (FS-CACHE-READS, FS-CACHE-WRITES) utilize the file system cache
in the client’s CPU and can result in a block read/write (FS-CACHE-RD-READ-REQS,
FS-CACHE-WT-READ-REQS, FS-CACHE-WRITE-REQS) between the cache and DP2.
Block reads and writes occur on cache block boundaries (except for the last cache block
of the file) where a cache block is 4 KB. Block read operations try to read ahead
(FS-PREFETCH-BLOCKS) to anticipate any need for the information in the immediate future.
The OSS file system controls cache use and might, for internal reasons, select to bypass
its use on a particular file open.
• When a pipe is remote from the sender or receiver, the pipe server in the CPU where the pipe
was created acts as an agent for the remote clients. Write and read requests result in messages
to the pipe server in the CPU where the pipe was created. The pipe server, in turn, performs
proxy pipe reads and writes to the pipe buffer on behalf of the remote client.
• Select() messages between client and pipe server and between pipe servers, occur only when
the client calling select() is running in a CPU other than where the pipe was created:
1. The client sends a select request to the pipe server that manages the pipe.
2. The pipe server replies immediately.
3. When the client’s read, write, or both can succeed, the pipe server sends a select ready
request to the pipe server in the client’s CPU.
4. That pipe server awakens the client, and the select() call completes.
• You can calculate the OSS cache miss rate as:
OSS cache miss rate = (FS-Cache-RD-Read-Reqs +
FS-Cache-WT-Read-Reqs +
FS-Cache-Write-Reqs)
-------------------------------------------------------------
(FS-Cache-Reads + FS-Cache-Writes)
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