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openSUSE:Step:15-SP1
xen.15649
libxl.add-option-to-disable-disk-cache-flushes-...
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File libxl.add-option-to-disable-disk-cache-flushes-in-qdisk.patch of Package xen.15649
https://bugzilla.novell.com/show_bug.cgi?id=879425 --- tools/libxl/libxl.c | 2 ++ tools/libxl/libxl.h | 12 ++++++++++++ tools/libxl/libxlu_disk.c | 2 ++ tools/libxl/libxlu_disk_i.h | 2 +- tools/libxl/libxlu_disk_l.l | 1 + 5 files changed, 18 insertions(+), 1 deletion(-) --- a/docs/man/xl-disk-configuration.5.pod +++ b/docs/man/xl-disk-configuration.5.pod @@ -344,6 +344,32 @@ can be used to disable "hole punching" f were intentionally created non-sparse to avoid fragmentation of the file. +=item B<suse-diskcache-disable-flush> + +=over 4 + +=item Description + +Request that the qemu block driver does not automatically flush written data to the backend storage. + +=item Supported values + +absent, present + +=item Mandatory + +No + +=item Default value + +absent + +=back + +This enables the '-disk cache=unsafe' mode inside qemu. +In this mode writes to the underlying blockdevice are delayed. +While using this option in production is dangerous, it improves performance during installation of a domU. + =back --- a/tools/libxl/libxl.h +++ b/tools/libxl/libxl.h @@ -386,6 +386,21 @@ #define LIBXL_HAVE_EXTENDED_VKB 1 /* + * The libxl_device_disk has no way to indicate that cache=unsafe is + * supposed to be used. Provide this knob without breaking the ABI. + * This is done by overloading struct libxl_device_disk->readwrite: + * readwrite == 0: disk is readonly, cache= does not matter + * readwrite == 1: disk is readwrite, backend driver may tweak cache= + * readwrite == MAGIC: disk is readwrite, backend driver should ignore + * flush requests from the frontend driver. + * Note: the macro with MAGIC is used by libvirt to decide if this patch is applied + */ +#define LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC 0x00006000U +#define LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK 0xffff0fffU +#define LIBXL_SUSE_IS_CACHE_UNSAFE(rw) (((rw) & ~LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK) == LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC) +#define LIBXL_SUSE_SET_CACHE_UNSAFE(rw) (((rw) & LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MASK) | LIBXL_HAVE_LIBXL_DEVICE_DISK_DISABLE_FLUSH_MAGIC) + +/* * libxl ABI compatibility * * The only guarantee which libxl makes regarding ABI compatibility --- a/tools/libxl/libxl_disk.c +++ b/tools/libxl/libxl_disk.c @@ -405,6 +405,8 @@ static void device_disk_add(libxl__egc * flexarray_append_pair(back, "discard-enable", libxl_defbool_val(disk->discard_enable) ? "1" : "0"); + if (LIBXL_SUSE_IS_CACHE_UNSAFE(disk->readwrite)) + flexarray_append_pair(back, "suse-diskcache-disable-flush", "1"); flexarray_append(front, "backend-id"); flexarray_append(front, GCSPRINTF("%d", disk->backend_domid)); --- a/tools/libxl/libxl_dm.c +++ b/tools/libxl/libxl_dm.c @@ -984,14 +984,27 @@ enum { LIBXL__COLO_SECONDARY, }; +static const char *qemu_cache_mode(const libxl_device_disk *disk) +{ + static const char cache_directsync[] = "directsync"; + static const char cache_writeback[] = "writeback"; + static const char cache_unsafe[] = "unsafe"; + + if (LIBXL_SUSE_IS_CACHE_UNSAFE(disk->readwrite)) + return cache_unsafe; + if (disk->direct_io_safe) + return cache_directsync; + return cache_writeback; +} + static char *qemu_disk_scsi_drive_string(libxl__gc *gc, const char *target_path, int unit, const char *format, const libxl_device_disk *disk, int colo_mode, const char **id_ptr) { char *drive = NULL; - char *common = GCSPRINTF("if=none,readonly=%s,cache=writeback", - disk->readwrite ? "off" : "on"); + char *common = GCSPRINTF("if=none,readonly=%s,cache=%s", + disk->readwrite ? "off" : "on", qemu_cache_mode(disk)); const char *exportname = disk->colo_export; const char *active_disk = disk->active_disk; const char *hidden_disk = disk->hidden_disk; @@ -1050,8 +1063,8 @@ static char *qemu_disk_ide_drive_string( switch (colo_mode) { case LIBXL__COLO_NONE: drive = GCSPRINTF - ("file=%s,if=ide,index=%d,media=disk,format=%s,cache=writeback", - target_path, unit, format); + ("file=%s,if=ide,index=%d,media=disk,format=%s,cache=%s", + target_path, unit, format, qemu_cache_mode(disk)); break; case LIBXL__COLO_PRIMARY: /* @@ -1064,13 +1077,14 @@ static char *qemu_disk_ide_drive_string( * vote-threshold=1 */ drive = GCSPRINTF( - "if=ide,index=%d,media=disk,cache=writeback,driver=quorum," + "if=ide,index=%d,media=disk,cache=%s,driver=quorum," "id=%s," "children.0.file.filename=%s," "children.0.driver=%s," "read-pattern=fifo," "vote-threshold=1", - unit, exportname, target_path, format); + unit, qemu_cache_mode(disk), + exportname, target_path, format); break; case LIBXL__COLO_SECONDARY: /* @@ -1084,7 +1098,7 @@ static char *qemu_disk_ide_drive_string( * file.backing.backing=exportname, */ drive = GCSPRINTF( - "if=ide,index=%d,id=top-colo,media=disk,cache=writeback," + "if=ide,index=%d,id=top-colo,media=disk,cache=%s," "driver=replication," "mode=secondary," "top-id=top-colo," @@ -1093,7 +1107,8 @@ static char *qemu_disk_ide_drive_string( "file.backing.driver=qcow2," "file.backing.file.filename=%s," "file.backing.backing=%s", - unit, active_disk, hidden_disk, exportname); + unit, qemu_cache_mode(disk), + active_disk, hidden_disk, exportname); break; default: abort(); @@ -1890,8 +1905,8 @@ static int libxl__build_device_model_arg return ERROR_INVAL; } flexarray_vappend(dm_args, "-drive", - GCSPRINTF("file=%s,if=none,id=ahcidisk-%d,format=%s,cache=writeback", - target_path, disk, format), + GCSPRINTF("file=%s,if=none,id=ahcidisk-%d,format=%s,cache=%s", + target_path, disk, format, qemu_cache_mode(&disks[i])), "-device", GCSPRINTF("ide-hd,bus=ahci0.%d,unit=0,drive=ahcidisk-%d", disk, disk), NULL); continue; --- a/tools/libxl/libxlu_disk.c +++ b/tools/libxl/libxlu_disk.c @@ -79,6 +79,8 @@ int xlu_disk_parse(XLU_Config *cfg, if (!disk->pdev_path || !strcmp(disk->pdev_path, "")) disk->format = LIBXL_DISK_FORMAT_EMPTY; } + if (disk->readwrite && dpc.suse_diskcache_disable_flush) + disk->readwrite = LIBXL_SUSE_SET_CACHE_UNSAFE(disk->readwrite); if (!disk->vdev) { xlu__disk_err(&dpc,0, "no vdev specified"); --- a/tools/libxl/libxlu_disk_i.h +++ b/tools/libxl/libxlu_disk_i.h @@ -10,7 +10,7 @@ typedef struct { void *scanner; YY_BUFFER_STATE buf; libxl_device_disk *disk; - int access_set, had_depr_prefix; + int access_set, suse_diskcache_disable_flush, had_depr_prefix; const char *spec; } DiskParseContext; --- a/tools/libxl/libxlu_disk_l.l +++ b/tools/libxl/libxlu_disk_l.l @@ -196,6 +196,7 @@ colo-port=[^,]*,? { STRIP(','); setcolop colo-export=[^,]*,? { STRIP(','); SAVESTRING("colo-export", colo_export, FROMEQUALS); } active-disk=[^,]*,? { STRIP(','); SAVESTRING("active-disk", active_disk, FROMEQUALS); } hidden-disk=[^,]*,? { STRIP(','); SAVESTRING("hidden-disk", hidden_disk, FROMEQUALS); } +suse-diskcache-disable-flush,? { DPC->suse_diskcache_disable_flush = 1; } /* the target magic parameter, eats the rest of the string */
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