Messages in this thread Patch in this message | | | From | Marc-André Lureau <> | Subject | [PATCH v16 11/11] RFC: fw_cfg: do DMA read operation | Date | Wed, 28 Feb 2018 16:06:15 +0100 |
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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.lureau@redhat.com> --- drivers/firmware/qemu_fw_cfg.c | 68 ++++++++++++++++++++++++++++++++++-------- 1 file changed, 55 insertions(+), 13 deletions(-)
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c index 14fedbeca724..db1cba4f99bd 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c @@ -66,7 +66,6 @@ static void fw_cfg_sel_endianness(u16 key) iowrite16(key, fw_cfg_reg_ctrl); } -#ifdef CONFIG_CRASH_CORE static inline bool fw_cfg_dma_enabled(void) { return (fw_cfg_rev & FW_CFG_VERSION_DMA) && fw_cfg_reg_dma; @@ -124,14 +123,49 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control) return ret; } -#endif + +/* 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 { + fw_cfg_sel_endianness(key); + 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 ssize_t fw_cfg_read_blob_io(u16 key, + void *buf, loff_t pos, size_t count) +{ + fw_cfg_sel_endianness(key); + while (pos-- > 0) + ioread8(fw_cfg_reg_data); + ioread8_rep(fw_cfg_reg_data, buf, count); + return count; +} /* read chunk of given fw_cfg blob (caller responsible for sanity-check) */ static ssize_t fw_cfg_read_blob(u16 key, - void *buf, loff_t pos, size_t count) + void *buf, loff_t pos, size_t count, + ssize_t (*readfn)(u16 key, void *buf, + loff_t pos, size_t count)) { u32 glk = -1U; acpi_status status; + ssize_t ret; /* If we have ACPI, ensure mutual exclusion against any potential * device access by the firmware, e.g. via AML methods: @@ -145,14 +179,19 @@ static ssize_t fw_cfg_read_blob(u16 key, } mutex_lock(&fw_cfg_dev_lock); - fw_cfg_sel_endianness(key); - while (pos-- > 0) - ioread8(fw_cfg_reg_data); - ioread8_rep(fw_cfg_reg_data, buf, count); + + /* fallback to IO if DMA is not available */ + if (readfn == fw_cfg_read_blob_dma && !fw_cfg_dma_enabled()) { + readfn = fw_cfg_read_blob_io; + } + + ret = readfn(key, buf, pos, count); + mutex_unlock(&fw_cfg_dev_lock); acpi_release_global_lock(glk); - return count; + + return ret; } #ifdef CONFIG_CRASH_CORE @@ -286,7 +325,7 @@ static int fw_cfg_do_platform_probe(struct platform_device *pdev) /* verify fw_cfg device signature */ if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, - 0, FW_CFG_SIG_SIZE) < 0 || + 0, FW_CFG_SIG_SIZE, fw_cfg_read_blob_io) < 0 || memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { fw_cfg_io_cleanup(); return -ENODEV; @@ -470,7 +509,9 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj, if (count > entry->size - pos) count = entry->size - pos; - return fw_cfg_read_blob(entry->select, buf, pos, count); + /* do not use DMA, virt_to_phys(buf) might not be ok */ + return fw_cfg_read_blob(entry->select, buf, pos, count, + fw_cfg_read_blob_io); } static struct bin_attribute fw_cfg_sysfs_attr_raw = { @@ -636,7 +677,7 @@ static int fw_cfg_register_dir_entries(void) size_t dir_size; ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files_count, - 0, sizeof(files_count)); + 0, sizeof(files_count), fw_cfg_read_blob_io); if (ret < 0) return ret; @@ -648,7 +689,7 @@ static int fw_cfg_register_dir_entries(void) return -ENOMEM; ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, - sizeof(files_count), dir_size); + sizeof(files_count), dir_size, fw_cfg_read_blob_dma); if (ret < 0) goto end; @@ -699,7 +740,8 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev) goto err_probe; /* get revision number, add matching top-level attribute */ - err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev)); + err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev), + fw_cfg_read_blob_io); if (err < 0) goto err_probe; -- 2.16.1.73.g5832b7e9f2
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