Hi On Wed, Feb 14, 2018 at 5:48 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > On Wed, Feb 14, 2018 at 03:18:50PM +0100, Marc-André Lureau wrote: >> Modify fw_cfg_read_blob() to use DMA if the device supports it. >> Return errors, because the operation may fail. >> >> So far, only one call in fw_cfg_register_dir_entries() is using >> kmalloc'ed buf and is thus clearly eligible to DMA read. >> >> Initially, I didn't implement DMA read to speed up boot time, but as a >> first step before introducing DMA write (since read operations were >> already presents). Even more, I didn't realize fw-cfg entries were >> being read by the kernel during boot by default. But actally fw-cfg >> entries are being populated during module probe. I knew DMA improved a >> lot bios boot time (the main reason the DMA interface was added >> afaik). Let see the time it would take to read the whole ACPI >> tables (128kb allocated) >> >> # time cat /sys/firmware/qemu_fw_cfg/by_name/etc/acpi/tables/raw >> - with DMA: sys 0m0.003s >> - without DMA (-global fw_cfg.dma_enabled=off): sys 0m7.674s >> >> FW_CFG_FILE_DIR (0x19) is the only "file" that is read during kernel >> boot to populate sysfs qemu_fw_cfg directory, and it is quite >> small (1-2kb). Since it does not expose itself, in order to measure >> the time it takes to read such small file, I took a comparable sized >> file of 2048 bytes and exposed it (-fw_cfg test,file=file with a >> modified read_raw enabling DMA) >> >> # perf stat -r 100 cat /sys/firmware/qemu_fw_cfg/by_name/test/raw >/dev/null >> - with DMA: >> 0.636037 task-clock (msec) # 0.141 CPUs utilized >> ( +- 1.19% ) >> - without DMA: >> 6.430128 task-clock (msec) # 0.622 CPUs utilized >> ( +- 0.22% ) >> >> That's a few msec saved during boot by enabling DMA read (the gain >> would be more substantial if other & bigger fw-cfg entries are read by >> others from sysfs, unfortunately, it's not clear if we can always >> enable DMA there) >> >> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> >> --- >> drivers/firmware/qemu_fw_cfg.c | 80 >> ++++++++++++++++++++++++++++++++++-------- >> 1 file changed, 66 insertions(+), 14 deletions(-) >> >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c >> index 69939e2529f2..ba9b907a4399 100644 >> --- a/drivers/firmware/qemu_fw_cfg.c >> +++ b/drivers/firmware/qemu_fw_cfg.c >> @@ -124,12 +124,46 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 >> length, u32 control) >> return ret; >> } >> >> +/* with acpi & dev locks taken */ >> +static ssize_t fw_cfg_read_blob_dma(u16 key, >> + void *buf, loff_t pos, size_t count) >> +{ >> + ssize_t ret; >> + >> + if (pos == 0) { >> + ret = fw_cfg_dma_transfer(buf, count, key << 16 >> + | FW_CFG_DMA_CTL_SELECT >> + | FW_CFG_DMA_CTL_READ); >> + } else { >> + iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); >> + ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP); >> + if (ret < 0) >> + return ret; >> + ret = fw_cfg_dma_transfer(buf, count, >> + FW_CFG_DMA_CTL_READ); >> + } >> + >> + return ret; >> +} >> + >> +/* with acpi & dev locks taken */ >> +static void fw_cfg_read_blob_io(u16 key, >> + void *buf, loff_t pos, size_t count) >> +{ >> + iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); >> + while (pos-- > 0) >> + ioread8(fw_cfg_reg_data); >> + ioread8_rep(fw_cfg_reg_data, buf, count); >> +} >> + >> /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */ >> -static inline void fw_cfg_read_blob(u16 key, >> - void *buf, loff_t pos, size_t count) >> +static ssize_t fw_cfg_read_blob(u16 key, >> + void *buf, loff_t pos, size_t count, >> + bool dma) >> { >> u32 glk = -1U; >> acpi_status status; >> + ssize_t ret = count; >> >> /* If we have ACPI, ensure mutual exclusion against any potential >> * device access by the firmware, e.g. via AML methods: >> @@ -139,17 +173,21 @@ static inline void fw_cfg_read_blob(u16 key, >> /* Should never get here */ >> WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n"); >> memset(buf, 0, count); >> - return; >> + return -EINVAL; >> } >> >> mutex_lock(&fw_cfg_dev_lock); >> - iowrite16(fw_cfg_sel_endianness(key), fw_cfg_reg_ctrl); >> - while (pos-- > 0) >> - ioread8(fw_cfg_reg_data); >> - ioread8_rep(fw_cfg_reg_data, buf, count); >> + if (dma && fw_cfg_dma_enabled()) { >> + ret = fw_cfg_read_blob_dma(key, buf, pos, count); >> + } else { >> + fw_cfg_read_blob_io(key, buf, pos, count); > > I'd set ret = count here.
Ok, why not. > >> + } >> + >> mutex_unlock(&fw_cfg_dev_lock); >> >> acpi_release_global_lock(glk); >> + >> + return ret; >> } >> >> #ifdef CONFIG_CRASH_CORE >> @@ -282,8 +320,9 @@ static int fw_cfg_do_platform_probe(struct >> platform_device *pdev) >> #endif >> >> /* verify fw_cfg device signature */ >> - fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE); >> - if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { >> + if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, >> + 0, FW_CFG_SIG_SIZE, false) < 0 || >> + memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { >> fw_cfg_io_cleanup(); >> return -ENODEV; >> } > > Rather than add dead code, how about a promise not to > fail if dma is disabled? Patch will be smaller then. Even with dma disabled, you could have a locking bug which was silently ignored before and is now taken into account. > >> @@ -466,8 +505,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, >> struct kobject *kobj, >> if (count > entry->size - pos) >> count = entry->size - pos; >> >> - fw_cfg_read_blob(entry->select, buf, pos, count); >> - return count; >> + /* do not use DMA, virt_to_phys(buf) might not be ok */ >> + return fw_cfg_read_blob(entry->select, buf, pos, count, false); >> } >> >> static struct bin_attribute fw_cfg_sysfs_attr_raw = { >> @@ -632,7 +671,12 @@ static int fw_cfg_register_dir_entries(void) >> struct fw_cfg_file *dir; >> size_t dir_size; >> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count, 0, >> sizeof(files.count)); >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files.count, >> + 0, sizeof(files.count), false); >> + if (ret < 0) { >> + return ret; >> + } >> + >> count = be32_to_cpu(files.count); >> dir_size = count * sizeof(struct fw_cfg_file); >> >> @@ -640,7 +684,11 @@ static int fw_cfg_register_dir_entries(void) >> if (!dir) >> return -ENOMEM; >> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(files.count), dir_size); >> + ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, >> + sizeof(files.count), dir_size, false); >> + if (ret < 0) { >> + goto end; >> + } >> >> for (i = 0; i < count; i++) { >> ret = fw_cfg_register_file(&dir[i]); >> @@ -648,6 +696,7 @@ static int fw_cfg_register_dir_entries(void) >> break; >> } >> >> +end: >> kfree(dir); >> return ret; >> } >> @@ -688,7 +737,10 @@ static int fw_cfg_sysfs_probe(struct platform_device >> *pdev) >> goto err_probe; >> >> /* get revision number, add matching top-level attribute */ >> - fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev)); >> + err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), false); >> + if (err < 0) { >> + goto err_probe; >> + } >> fw_cfg_rev = le32_to_cpu(rev); >> err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr); >> if (err) >> -- >> 2.16.1.73.g5832b7e9f2