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of the trampoline logic. The trampoline logic of 3.17 required a descriptor for every function that is registered to be traced and uses a trampoline. Currently, only the function graph tracer uses a trampoline, but if you were to trace all 32,000 (give or take a few thousand) functions with the function graph tracer, it would create 32,000 descriptors to let us know that there's a trampoline associated with it. This takes up a bit of memory when there's a better way to do it. The redesign now reuses the ftrace_ops' (what registers the function graph tracer) hash tables. The hash tables tell ftrace what the tracer wants to trace or doesn't want to trace. There's two of them: one that tells us what to trace, the other tells us what not to trace. If the first one is empty, it means all functions should be traced, otherwise only the ones that are listed should be. The second hash table tells us what not to trace, and if it is empty, all functions may be traced, and if there's any listed, then those should not be traced even if they exist in the first hash table. It took a bit of massaging, but now these hashes can be used to keep track of what has a trampoline and what does not, and allows the ftrace accounting to work. Now we can trace all functions when using the function graph trampoline, and avoid needing to create any special descriptors to hold all the functions that are being traced. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAABAgAGBQJUMwp6AAoJEKQekfcNnQGuIoAIAIsqvTYAnULyzKKCweEZYUfb XJzz6cN5FPGSXkoeda1ZvnfOlHjFRrWNXzXMB0jZYR2hU++pe3xjtghaNzvbRcyV wlwDUTsnz235OcOuFEspIwBamhtah96Coiwf/2z/2q6srXlHd/1TrqXB+Fpj1tEK BkAViGDUEdq/eLZX7nGen36cTb5gpNqV9NjY1CVAK6bSkU/xXk/ArqFy1qy0MPnc z/9bXdIf+Z6VnG/IzwRc2rwiMFuD1+lpjLuHEqagoHp1D4teCjWPSJl1EKCVAS40 GaCOTUZi92zIVgx8Bb28TglSla9MN65CO3E8dw6hlXUIsNz1p0eavpctnC6ac/Y= =vDpP -----END PGP SIGNATURE----- Merge tag 'trace-3.18' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull tracing updates from Steven Rostedt: "This set has a few minor updates, but the big change is the redesign of the trampoline logic. The trampoline logic of 3.17 required a descriptor for every function that is registered to be traced and uses a trampoline. Currently, only the function graph tracer uses a trampoline, but if you were to trace all 32,000 (give or take a few thousand) functions with the function graph tracer, it would create 32,000 descriptors to let us know that there's a trampoline associated with it. This takes up a bit of memory when there's a better way to do it. The redesign now reuses the ftrace_ops' (what registers the function graph tracer) hash tables. The hash tables tell ftrace what the tracer wants to trace or doesn't want to trace. There's two of them: one that tells us what to trace, the other tells us what not to trace. If the first one is empty, it means all functions should be traced, otherwise only the ones that are listed should be. The second hash table tells us what not to trace, and if it is empty, all functions may be traced, and if there's any listed, then those should not be traced even if they exist in the first hash table. It took a bit of massaging, but now these hashes can be used to keep track of what has a trampoline and what does not, and allows the ftrace accounting to work. Now we can trace all functions when using the function graph trampoline, and avoid needing to create any special descriptors to hold all the functions that are being traced" * tag 'trace-3.18' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: ftrace: Only disable ftrace_enabled to test buffer in selftest ftrace: Add sanity check when unregistering last ftrace_ops kernel: trace_syscalls: Replace rcu_assign_pointer() with RCU_INIT_POINTER() tracing: generate RCU warnings even when tracepoints are disabled ftrace: Replace tramp_hash with old_*_hash to save space ftrace: Annotate the ops operation on update ftrace: Grab any ops for a rec for enabled_functions output ftrace: Remove freeing of old_hash from ftrace_hash_move() ftrace: Set callback to ftrace_stub when no ops are registered ftrace: Add helper function ftrace_ops_get_func() ftrace: Add separate function for non recursive callbacks |
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