Messages in this thread |  | | Date | Mon, 12 Feb 2018 05:30:03 +0200 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH v13 4/4] RFC: fw_cfg: do DMA read operation |
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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.
> #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.
> @@ -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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