dlt-system: Avoid expensive getpid() syscalls #717
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Thanks for the finding, do you have any references for us to refer @aleixpol |
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I'm sorry, what references are you referring to? |
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I found doc of getpid enter and exit syscall on internet, thanks. |
include/dlt/dlt_user.h.in
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| @@ -271,6 +271,10 @@ typedef struct | |||
| #ifdef DLT_TRACE_LOAD_CTRL_ENABLE | |||
| pthread_rwlock_t trace_load_limit_lock; | |||
| #endif | |||
| // Since glibc 2.25, getpid() no longer caches the PID, instead performing a | |||
| // full syscall every time. This means we're performing a full syscall | |||
| // roundtrip for *every* *single* *log* *message* on the system. | |||
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"Kindly please shorten these lines for variable definitions and align your comment with the standard used in the DltUser struct ?
Ex: /* Local DltUser process identifier */
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Do we still wait for author to refactor here? if yes then @aleixpol can you push latest patch?
src/lib/dlt_user.c
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| @@ -4011,7 +4014,11 @@ DltReturnValue dlt_user_log_send_log(DltContextData *log, const int mtype, int * | |||
| /* send session id */ | |||
| if (dlt_user.with_session_id) { | |||
| msg.standardheader->htyp |= DLT_HTYP_WSID; | |||
| msg.headerextra.seid = (uint32_t) getpid(); | |||
| // 99.99999% of the time, we'll already have a PID set. | |||
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Can you remove this comment? You're right, but it is better to remove this comment.
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Yeah we actually dont need it, unless any dev really want to know the func call then gcc doc already mentioned in detail
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Hello @aleixpol |
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GCC reference: __builtin_expect() |
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Hello @aleixpol , hello @minminlittleshrimp , hello @Bichdao021195 , hello @lti9hc , i have verified the change with the test code at: dlt-daemon/src/tests/dlt-test-fork-handler.c |
That's cool, will approve and merge after latest patchset uploaded |
Since glibc 2.25, getpid() no longer caches the PID, instead performing a full syscall every time. This means we're performing a full syscall roundtrip for *every* *single* *log* *message* on the system. This patch caches the result of getpid() when appropriate, avoiding unnessicary syscalls. Signed-off-by: Aleix Pol Gonzalez <[email protected]>
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Since glibc 2.25, getpid() no longer caches the PID, instead performing a full syscall every time. This means we're performing a full syscall roundtrip for every single log message on the system.
This patch caches the result of getpid() when appropriate, avoiding unnessicary syscalls.