Messages in this thread Patch in this message | | | From | Marc-André Lureau <> | Subject | [PATCH v14 9/9] RFC: fw_cfg: do DMA read operation | Date | Wed, 14 Feb 2018 15:18:50 +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 | 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); + } + 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; } @@ -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
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