Messages in this thread | | | From | Marc-Andre Lureau <> | Date | Mon, 12 Feb 2018 13:16:40 +0100 | Subject | Re: [PATCH v13 4/4] RFC: fw_cfg: do DMA read operation |
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Hi
On Mon, Feb 12, 2018 at 4:30 AM, Michael S. Tsirkin <mst@redhat.com> wrote: > On Wed, Feb 07, 2018 at 02:35:25AM +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.lureau@redhat.com> >> --- >> drivers/firmware/qemu_fw_cfg.c | 47 ++++++++++++++++++++++++++++++------------ >> 1 file changed, 34 insertions(+), 13 deletions(-) >> >> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c >> index fd576ba7b337..3721dc868a2b 100644 >> --- a/drivers/firmware/qemu_fw_cfg.c >> +++ b/drivers/firmware/qemu_fw_cfg.c >> @@ -150,11 +150,13 @@ static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control) >> } >> >> /* 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: >> @@ -164,17 +166,36 @@ 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()) { >> + 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) >> + goto end; >> + ret = fw_cfg_dma_transfer(buf, count, >> + FW_CFG_DMA_CTL_READ); >> + } >> + } else { >> + 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); >> + } >> + >> +end: >> mutex_unlock(&fw_cfg_dev_lock); >> >> acpi_release_global_lock(glk); >> + >> + return ret; >> } >> > > These two functions share no common code at all. > Pls name the dma one fw_cfg_dma_read or something like this, > cleaner than a flag.
They share arguments, ACPI locking, error handling, cleanup. But they also allow to abstract read over dma-capable and non-dma capable. I'll split both cases in two functions.
> >> #ifdef CONFIG_CRASH_CORE >> @@ -307,7 +328,7 @@ 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); >> + fw_cfg_read_blob(FW_CFG_SIGNATURE, sig, 0, FW_CFG_SIG_SIZE, false); >> if (memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) { >> fw_cfg_io_cleanup(); >> return -ENODEV; > > BTW it looks like fw_cfg_read_blob can fail and that failure isn't > handled properly here.
ok
> >> @@ -494,8 +515,8 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj, >> if (count > entry->f.size - pos) >> count = entry->f.size - pos; >> >> - fw_cfg_read_blob(entry->f.select, buf, pos, count); >> - return count; >> + /* do not use DMA, virt_to_phys(buf) might not be ok */ >> + return fw_cfg_read_blob(entry->f.select, buf, pos, count, false); >> } >> >> static struct bin_attribute fw_cfg_sysfs_attr_raw = { >> @@ -656,7 +677,7 @@ 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, &count, 0, sizeof(count)); >> + fw_cfg_read_blob(FW_CFG_FILE_DIR, &count, 0, sizeof(count), false); >> count = be32_to_cpu(count); >> dir_size = count * sizeof(struct fw_cfg_file); >> >> @@ -664,7 +685,7 @@ static int fw_cfg_register_dir_entries(void) >> if (!dir) >> return -ENOMEM; >> >> - fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size); >> + fw_cfg_read_blob(FW_CFG_FILE_DIR, dir, sizeof(count), dir_size, true); >> >> for (i = 0; i < count; i++) { >> dir[i].size = be32_to_cpu(dir[i].size); >> @@ -713,7 +734,7 @@ 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, &fw_cfg_rev, 0, sizeof(fw_cfg_rev)); >> + fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev), false); >> fw_cfg_rev = le32_to_cpu(fw_cfg_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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