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Commit a7c4bd1a authored by Tim Murray's avatar Tim Murray
Browse files

dumpstate: improve performance 

Two changes:

1. There were some seemingly-unnecessary fsyncs scattered throughout
dumpstate. Remove those.

2. Profiling revealed that a significant amount of dumpstate's CPU
overhead was spent copying/destroying PTEs around fork/exec. Switch to
vfork() to avoid the PTE copies.

Test: bug reports work
Bug: 215574756
Change-Id: Ib202fd5c8d1f37548ee53bd64eaf4e114098a062
parent 00ff352c

cmds/dumpstate/DumpstateUtil.cpp

+2 −6
Original line number Diff line number Diff line
@@ -247,7 +247,6 @@ int DumpFileToFd(int out_fd, const std::string& title, const std::string& path) 
            dprintf(out_fd, "*** Error dumping %s (%s): %s\n", path.c_str(), title.c_str(),

                    strerror(err));

        }

        fsync(out_fd);

        return -1;

    }

    return DumpFileFromFdToFd(title, path, fd.get(), out_fd, PropertiesHelper::IsDryRun());
@@ -295,7 +294,6 @@ int RunCommandToFd(int fd, const std::string& title, const std::vector<std::stri 


    if (!title.empty()) {

        dprintf(fd, "------ %s (%s) ------\n", title.c_str(), command);

        fsync(fd);

    }



    const std::string& logging_message = options.LoggingMessage();
@@ -314,14 +312,13 @@ int RunCommandToFd(int fd, const std::string& title, const std::vector<std::stri 
            // There is no title, but we should still print a dry-run message

            dprintf(fd, "%s: skipped on dry run\n", command_string.c_str());

        }

        fsync(fd);

        return 0;

    }



    const char* path = args[0];



    uint64_t start = Nanotime();

    pid_t pid = fork();

    pid_t pid = vfork();



    /* handle error case */

    if (pid < 0) {
@@ -338,7 +335,7 @@ int RunCommandToFd(int fd, const std::string& title, const std::vector<std::stri 
                        strerror(errno));

            }

            MYLOGE("*** could not drop root before running %s: %s\n", command, strerror(errno));

            return -1;

            _exit(EXIT_FAILURE);

        }



        if (options.ShouldCloseAllFileDescriptorsOnExec()) {
@@ -391,7 +388,6 @@ int RunCommandToFd(int fd, const std::string& title, const std::vector<std::stri 
    /* handle parent case */

    int status;

    bool ret = waitpid_with_timeout(pid, options.TimeoutInMs(), &status);

    fsync(fd);



    uint64_t elapsed = Nanotime() - start;

    if (!ret) {