diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/ubifs.txt | 28 | ||||
| -rw-r--r-- | Documentation/mmc/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/mmc/mmc-async-req.txt | 87 | ||||
| -rw-r--r-- | Documentation/virtual/lguest/lguest.c | 47 | ||||
| -rw-r--r-- | Documentation/x86/boot.txt | 2 |
5 files changed, 106 insertions, 60 deletions
diff --git a/Documentation/filesystems/ubifs.txt b/Documentation/filesystems/ubifs.txt index 8e4fab639d9..a0a61d2f389 100644 --- a/Documentation/filesystems/ubifs.txt +++ b/Documentation/filesystems/ubifs.txt @@ -111,34 +111,6 @@ The following is an example of the kernel boot arguments to attach mtd0 to UBI and mount volume "rootfs": ubi.mtd=0 root=ubi0:rootfs rootfstype=ubifs - -Module Parameters for Debugging -=============================== - -When UBIFS has been compiled with debugging enabled, there are 2 module -parameters that are available to control aspects of testing and debugging. - -debug_chks Selects extra checks that UBIFS can do while running: - - Check Flag value - - General checks 1 - Check Tree Node Cache (TNC) 2 - Check indexing tree size 4 - Check orphan area 8 - Check old indexing tree 16 - Check LEB properties (lprops) 32 - Check leaf nodes and inodes 64 - -debug_tsts Selects a mode of testing, as follows: - - Test mode Flag value - - Failure mode for recovery testing 4 - -For example, set debug_chks to 3 to enable general and TNC checks. - - References ========== diff --git a/Documentation/mmc/00-INDEX b/Documentation/mmc/00-INDEX index 93dd7a71407..a9ba6720ffd 100644 --- a/Documentation/mmc/00-INDEX +++ b/Documentation/mmc/00-INDEX @@ -4,3 +4,5 @@ mmc-dev-attrs.txt - info on SD and MMC device attributes mmc-dev-parts.txt - info on SD and MMC device partitions +mmc-async-req.txt + - info on mmc asynchronous requests diff --git a/Documentation/mmc/mmc-async-req.txt b/Documentation/mmc/mmc-async-req.txt new file mode 100644 index 00000000000..ae1907b10e4 --- /dev/null +++ b/Documentation/mmc/mmc-async-req.txt @@ -0,0 +1,87 @@ +Rationale +========= + +How significant is the cache maintenance overhead? +It depends. Fast eMMC and multiple cache levels with speculative cache +pre-fetch makes the cache overhead relatively significant. If the DMA +preparations for the next request are done in parallel with the current +transfer, the DMA preparation overhead would not affect the MMC performance. +The intention of non-blocking (asynchronous) MMC requests is to minimize the +time between when an MMC request ends and another MMC request begins. +Using mmc_wait_for_req(), the MMC controller is idle while dma_map_sg and +dma_unmap_sg are processing. Using non-blocking MMC requests makes it +possible to prepare the caches for next job in parallel with an active +MMC request. + +MMC block driver +================ + +The mmc_blk_issue_rw_rq() in the MMC block driver is made non-blocking. +The increase in throughput is proportional to the time it takes to +prepare (major part of preparations are dma_map_sg() and dma_unmap_sg()) +a request and how fast the memory is. The faster the MMC/SD is the +more significant the prepare request time becomes. Roughly the expected +performance gain is 5% for large writes and 10% on large reads on a L2 cache +platform. In power save mode, when clocks run on a lower frequency, the DMA +preparation may cost even more. As long as these slower preparations are run +in parallel with the transfer performance won't be affected. + +Details on measurements from IOZone and mmc_test +================================================ + +https://wiki.linaro.org/WorkingGroups/Kernel/Specs/StoragePerfMMC-async-req + +MMC core API extension +====================== + +There is one new public function mmc_start_req(). +It starts a new MMC command request for a host. The function isn't +truly non-blocking. If there is an ongoing async request it waits +for completion of that request and starts the new one and returns. It +doesn't wait for the new request to complete. If there is no ongoing +request it starts the new request and returns immediately. + +MMC host extensions +=================== + +There are two optional members in the mmc_host_ops -- pre_req() and +post_req() -- that the host driver may implement in order to move work +to before and after the actual mmc_host_ops.request() function is called. +In the DMA case pre_req() may do dma_map_sg() and prepare the DMA +descriptor, and post_req() runs the dma_unmap_sg(). + +Optimize for the first request +============================== + +The first request in a series of requests can't be prepared in parallel +with the previous transfer, since there is no previous request. +The argument is_first_req in pre_req() indicates that there is no previous +request. The host driver may optimize for this scenario to minimize +the performance loss. A way to optimize for this is to split the current +request in two chunks, prepare the first chunk and start the request, +and finally prepare the second chunk and start the transfer. + +Pseudocode to handle is_first_req scenario with minimal prepare overhead: + +if (is_first_req && req->size > threshold) + /* start MMC transfer for the complete transfer size */ + mmc_start_command(MMC_CMD_TRANSFER_FULL_SIZE); + + /* + * Begin to prepare DMA while cmd is being processed by MMC. + * The first chunk of the request should take the same time + * to prepare as the "MMC process command time". + * If prepare time exceeds MMC cmd time + * the transfer is delayed, guesstimate max 4k as first chunk size. + */ + prepare_1st_chunk_for_dma(req); + /* flush pending desc to the DMAC (dmaengine.h) */ + dma_issue_pending(req->dma_desc); + + prepare_2nd_chunk_for_dma(req); + /* + * The second issue_pending should be called before MMC runs out + * of the first chunk. If the MMC runs out of the first data chunk + * before this call, the transfer is delayed. + */ + dma_issue_pending(req->dma_desc); diff --git a/Documentation/virtual/lguest/lguest.c b/Documentation/virtual/lguest/lguest.c index cd9d6af61d0..043bd7df313 100644 --- a/Documentation/virtual/lguest/lguest.c +++ b/Documentation/virtual/lguest/lguest.c @@ -51,7 +51,7 @@ #include <asm/bootparam.h> #include "../../../include/linux/lguest_launcher.h" /*L:110 - * We can ignore the 42 include files we need for this program, but I do want + * We can ignore the 43 include files we need for this program, but I do want * to draw attention to the use of kernel-style types. * * As Linus said, "C is a Spartan language, and so should your naming be." I @@ -65,7 +65,6 @@ typedef uint16_t u16; typedef uint8_t u8; /*:*/ -#define PAGE_PRESENT 0x7 /* Present, RW, Execute */ #define BRIDGE_PFX "bridge:" #ifndef SIOCBRADDIF #define SIOCBRADDIF 0x89a2 /* add interface to bridge */ @@ -861,8 +860,10 @@ static void console_output(struct virtqueue *vq) /* writev can return a partial write, so we loop here. */ while (!iov_empty(iov, out)) { int len = writev(STDOUT_FILENO, iov, out); - if (len <= 0) - err(1, "Write to stdout gave %i", len); + if (len <= 0) { + warn("Write to stdout gave %i (%d)", len, errno); + break; + } iov_consume(iov, out, len); } @@ -898,7 +899,7 @@ static void net_output(struct virtqueue *vq) * same format: what a coincidence! */ if (writev(net_info->tunfd, iov, out) < 0) - errx(1, "Write to tun failed?"); + warnx("Write to tun failed (%d)?", errno); /* * Done with that one; wait_for_vq_desc() will send the interrupt if @@ -955,7 +956,7 @@ static void net_input(struct virtqueue *vq) */ len = readv(net_info->tunfd, iov, in); if (len <= 0) - err(1, "Failed to read from tun."); + warn("Failed to read from tun (%d).", errno); /* * Mark that packet buffer as used, but don't interrupt here. We want @@ -1093,9 +1094,10 @@ static void update_device_status(struct device *dev) warnx("Device %s configuration FAILED", dev->name); if (dev->running) reset_device(dev); - } else if (dev->desc->status & VIRTIO_CONFIG_S_DRIVER_OK) { - if (!dev->running) - start_device(dev); + } else { + if (dev->running) + err(1, "Device %s features finalized twice", dev->name); + start_device(dev); } } @@ -1120,25 +1122,11 @@ static void handle_output(unsigned long addr) return; } - /* - * Devices *can* be used before status is set to DRIVER_OK. - * The original plan was that they would never do this: they - * would always finish setting up their status bits before - * actually touching the virtqueues. In practice, we allowed - * them to, and they do (eg. the disk probes for partition - * tables as part of initialization). - * - * If we see this, we start the device: once it's running, we - * expect the device to catch all the notifications. - */ + /* Devices should not be used before features are finalized. */ for (vq = i->vq; vq; vq = vq->next) { if (addr != vq->config.pfn*getpagesize()) continue; - if (i->running) - errx(1, "Notification on running %s", i->name); - /* This just calls create_thread() for each virtqueue */ - start_device(i); - return; + errx(1, "Notification on %s before setup!", i->name); } } @@ -1370,7 +1358,7 @@ static void setup_console(void) * --sharenet=<name> option which opens or creates a named pipe. This can be * used to send packets to another guest in a 1:1 manner. * - * More sopisticated is to use one of the tools developed for project like UML + * More sophisticated is to use one of the tools developed for project like UML * to do networking. * * Faster is to do virtio bonding in kernel. Doing this 1:1 would be @@ -1380,7 +1368,7 @@ static void setup_console(void) * multiple inter-guest channels behind one interface, although it would * require some manner of hotplugging new virtio channels. * - * Finally, we could implement a virtio network switch in the kernel. + * Finally, we could use a virtio network switch in the kernel, ie. vhost. :*/ static u32 str2ip(const char *ipaddr) @@ -2017,10 +2005,7 @@ int main(int argc, char *argv[]) /* Tell the entry path not to try to reload segment registers. */ boot->hdr.loadflags |= KEEP_SEGMENTS; - /* - * We tell the kernel to initialize the Guest: this returns the open - * /dev/lguest file descriptor. - */ + /* We tell the kernel to initialize the Guest. */ tell_kernel(start); /* Ensure that we terminate if a device-servicing child dies. */ diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt index 9b7221a86df..7c3a8801b7c 100644 --- a/Documentation/x86/boot.txt +++ b/Documentation/x86/boot.txt @@ -674,7 +674,7 @@ Protocol: 2.10+ Field name: init_size Type: read -Offset/size: 0x25c/4 +Offset/size: 0x260/4 This field indicates the amount of linear contiguous memory starting at the kernel runtime start address that the kernel needs before it |