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f043683713
Using writev here is 20-40% faster than three write syscalls in succession for smaller (1-10k) objects in the delta base cache. This advantage decreases as object sizes approach pipe size (64k on Linux). writev reduces wakeups and syscalls on the read side as well: each write(2) syscall may trigger one or more corresponding read(2) syscalls in the reader. Attempting atomicity in the writer via writev also reduces the likelyhood of non-blocking readers failing with EAGAIN and having to call poll||select before attempting to read again. Unfortunately, this turns into a small (1-3%) slowdown for gigantic objects of a megabyte or more even with after increasing pipe size to 1MB via the F_SETPIPE_SZ fcntl(2) op. This slowdown is acceptable to me since the vast majority of objects are 64K or less for projects I've looked at. Relying on stdio buffering and fflush(3) after each response was considered for users without --buffer, but historically cat-file defaults to being compatible with non-blocking stdout and able to poll(2) after hitting EAGAIN on write(2). Using stdio on files with the O_NONBLOCK flag is (AFAIK) unspecified and likely subject to portability problems and thus avoided. Signed-off-by: Eric Wong <e@80x24.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
81 lines
2.5 KiB
C
81 lines
2.5 KiB
C
#ifndef WRITE_OR_DIE_H
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#define WRITE_OR_DIE_H
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void maybe_flush_or_die(FILE *, const char *);
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__attribute__((format (printf, 2, 3)))
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void fprintf_or_die(FILE *, const char *fmt, ...);
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void fwrite_or_die(FILE *f, const void *buf, size_t count);
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void fflush_or_die(FILE *f);
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void write_or_die(int fd, const void *buf, size_t count);
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void writev_or_die(int fd, struct git_iovec *, int iovcnt);
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void fwritev_or_die(FILE *, const struct git_iovec *, int iovcnt);
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/*
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* These values are used to help identify parts of a repository to fsync.
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* FSYNC_COMPONENT_NONE identifies data that will not be a persistent part of the
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* repository and so shouldn't be fsynced.
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*/
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enum fsync_component {
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FSYNC_COMPONENT_NONE,
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FSYNC_COMPONENT_LOOSE_OBJECT = 1 << 0,
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FSYNC_COMPONENT_PACK = 1 << 1,
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FSYNC_COMPONENT_PACK_METADATA = 1 << 2,
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FSYNC_COMPONENT_COMMIT_GRAPH = 1 << 3,
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FSYNC_COMPONENT_INDEX = 1 << 4,
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FSYNC_COMPONENT_REFERENCE = 1 << 5,
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};
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#define FSYNC_COMPONENTS_OBJECTS (FSYNC_COMPONENT_LOOSE_OBJECT | \
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FSYNC_COMPONENT_PACK)
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#define FSYNC_COMPONENTS_DERIVED_METADATA (FSYNC_COMPONENT_PACK_METADATA | \
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FSYNC_COMPONENT_COMMIT_GRAPH)
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#define FSYNC_COMPONENTS_DEFAULT ((FSYNC_COMPONENTS_OBJECTS | \
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FSYNC_COMPONENTS_DERIVED_METADATA) & \
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~FSYNC_COMPONENT_LOOSE_OBJECT)
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#define FSYNC_COMPONENTS_COMMITTED (FSYNC_COMPONENTS_OBJECTS | \
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FSYNC_COMPONENT_REFERENCE)
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#define FSYNC_COMPONENTS_ADDED (FSYNC_COMPONENTS_COMMITTED | \
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FSYNC_COMPONENT_INDEX)
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#define FSYNC_COMPONENTS_ALL (FSYNC_COMPONENT_LOOSE_OBJECT | \
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FSYNC_COMPONENT_PACK | \
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FSYNC_COMPONENT_PACK_METADATA | \
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FSYNC_COMPONENT_COMMIT_GRAPH | \
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FSYNC_COMPONENT_INDEX | \
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FSYNC_COMPONENT_REFERENCE)
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#ifndef FSYNC_COMPONENTS_PLATFORM_DEFAULT
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#define FSYNC_COMPONENTS_PLATFORM_DEFAULT FSYNC_COMPONENTS_DEFAULT
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#endif
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/* IO helper functions */
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void fsync_or_die(int fd, const char *);
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int fsync_component(enum fsync_component component, int fd);
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void fsync_component_or_die(enum fsync_component component, int fd, const char *msg);
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/*
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* A bitmask indicating which components of the repo should be fsynced.
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*/
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extern enum fsync_component fsync_components;
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extern int fsync_object_files;
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extern int use_fsync;
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enum fsync_method {
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FSYNC_METHOD_FSYNC,
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FSYNC_METHOD_WRITEOUT_ONLY,
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FSYNC_METHOD_BATCH,
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};
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extern enum fsync_method fsync_method;
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static inline int batch_fsync_enabled(enum fsync_component component)
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{
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return (fsync_components & component) && (fsync_method == FSYNC_METHOD_BATCH);
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}
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#endif /* WRITE_OR_DIE_H */
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