Date: Mon, 9 Jun 1997 23:45:22 +0200 (MET DST) From: Guenther Kelleter X-Sender: guenther@pc7390 To: linux-m68k@phil.uni-sb.de Subject: Re: L68K: fs affair (was: Quantum Fireball problems.) In-Reply-To: <9706062317.AA13442@faui21.informatik.uni-erlangen.de> Sender: owner-linux-m68k@phil.uni-sb.de Reply-To: linux-m68k@phil.uni-sb.de On Sat, 7 Jun 1997, Roman Hodek wrote: > What's so bad about the Falcon is that it can't do scatter-gather. Let > me explain: The Linux buffer cache breaks all disk requests down into > 1k chunks (usually), the size of a buffer. These buffers are usually > discontiguous in memory. Scatter-gather is now the method to merge > requests for buffers that don't follow one another in memory into one > command for the disk. This saves a lot of time (overhead of command, > message, status, bus free phases, ...) On a TT, this works rather > fine. But the Falcon SCSI design is broken, because the DMA can't > interrupt itself if it's finished. Due to that, we can't reprogram the > DMA for a different destination address during a command. There are > two solutions for this: Either make that sh*t DMA interrupt, or put > all buffer one after another in memory. Something like the latter is > done under TOS... Hey! I think it's time for a little patch to improve SCSI performance on Falcons slightly, which I'm using since more than half a year now without any problems. This one adds one more parameter to the kernel option `atascsi'. If set to > 0 then clustering of continuous blocks in memory is enabled, but only if there's no memory outside the DMA-able area (i.e. >= 16MB on Falcon), since this would require a larger bounce buffer than the currently available 4K sized buffer. I use it with a `Magnum FAST RAM Card'. --- Documentation/m68k/kernel-options.txt.~1~ Sat May 17 15:37:05 1997 +++ Documentation/m68k/kernel-options.txt Mon Jun 9 23:23:50 1997 @@ -575,7 +575,8 @@ 4.4) atascsi= ------------- -Syntax: atascsi=[,[,[,[,]]]] +Syntax: atascsi=[,[,[,[,[, + ]]]]] This option sets some parameters for the Atari native SCSI driver. Generally, any number of arguments can be omitted from the end. And @@ -636,6 +637,20 @@ one LUN, and the SCSI device itself orders the requests so they can be performed in optimal order. Not all SCSI devices support tagged queuing (:-(). + + : + Normally SCSI DMA transfers on the Atari Falcon are only done in + 1K chunks even if blocks are contiguous in memory, due to the broken + DMA design which is not capable of scatter-gather. If you have a Falcon + without `FAST-RAM' above 16MB (e.g. Magnum RAM Card), you can turn on + clustering of contiguous blocks > 1K, so that they are transferred + with only one SCSI command and one setup of the DMA. + Clustering improves SCSI performance on machines which don't support + scatter-gather. + + 0 turns off clustering, all other values > 0 turn on clustering if + there is no memory block present outside the DMA-able memory area. + Default is `off'. --- drivers/scsi/atari_scsi.c.~1~ Thu May 22 23:37:11 1997 +++ drivers/scsi/atari_scsi.c Mon Jun 9 23:01:02 1997 @@ -252,6 +252,8 @@ #endif static int setup_hostid = -1; MODULE_PARM(setup_hostid, "i"); +static int setup_use_clustering = -1; +MODULE_PARM(setup_use_clustering, "i"); #if defined(REAL_DMA) @@ -610,7 +612,7 @@ } while(0) -int atari_scsi_detect (Scsi_Host_Template *host) +__initfunc(int atari_scsi_detect (Scsi_Host_Template *host)) { static int called = 0; struct Scsi_Host *instance; @@ -680,16 +682,7 @@ atari_dma_orig_addr = 0; } #endif - instance = scsi_register (host, sizeof (struct NCR5380_hostdata)); - atari_scsi_host = instance; - /* Set irq to 0, to avoid that the mid-level code disables our interrupt - * during queue_command calls. This is completely unnecessary, and even - * worse causes bad problems on the Falcon, where the int is shared with - * IDE and floppy! */ - instance->irq = 0; - atari_scsi_reset_boot(); - NCR5380_init (instance, 0); if (IS_A_TT()) { @@ -734,20 +727,48 @@ atari_dma_stram_mask = (ATARIHW_PRESENT(EXTD_DMA) ? 0x00000000 : 0xff000000); #endif + /* Since Falcon cannot scatter-gather: Use clustering for + * contiguous requests, this is safe only if all RAM is DMA-able + * (s[drt].c is broken w.r.t. bounce buffers on m68k, + * see the usage of ISA_DMA_THRESHOLD). + */ + if (setup_use_clustering == 1) { + int i; + host->use_clustering = ENABLE_CLUSTERING; +#ifdef REAL_DMA + for (i=0; iuse_clustering = DISABLE_CLUSTERING; + break; + } +#endif + } } - printk(KERN_INFO "scsi%d: options CAN_QUEUE=%d CMD_PER_LUN=%d SCAT-GAT=%d " + instance = scsi_register(host, sizeof (struct NCR5380_hostdata)); + atari_scsi_host = instance; + /* Set irq to 0, to avoid that the mid-level code disables our interrupt + * during queue_command calls. This is completely unnecessary, and even + * worse causes bad problems on the Falcon, where the int is shared with + * IDE and floppy! */ + instance->irq = 0; + NCR5380_init(instance, 0); + + printk(KERN_INFO "scsi%d: options CAN_QUEUE=%d CMD_PER_LUN=%d SCAT-GAT=%d" #ifdef SUPPORT_TAGS - "TAGGED-QUEUING=%s " + " TAGGED-QUEUING=%s" #endif - "HOSTID=%d", - instance->host_no, instance->hostt->can_queue, - instance->hostt->cmd_per_lun, - instance->hostt->sg_tablesize, + " CLUSTERING=%s" + " HOSTID=%d" + "\n" KERN_INFO " ", + instance->host_no, instance->can_queue, + instance->cmd_per_lun, instance->sg_tablesize, #ifdef SUPPORT_TAGS - setup_use_tagged_queuing ? "yes" : "no", + setup_use_tagged_queuing ? "yes" : "no", #endif - instance->hostt->this_id ); + instance->use_clustering == ENABLE_CLUSTERING ? "yes" : "no", + instance->this_id); NCR5380_print_options (instance); printk ("\n"); @@ -769,7 +790,8 @@ __initfunc(void atari_scsi_setup( char *str, int *ints )) { /* Format of atascsi parameter is: - * atascsi=,,,, + * atascsi=,,,, + * , * Defaults depend on TT or Falcon, hostid determined at run time. * Negative values mean don't change. */ @@ -826,6 +848,10 @@ setup_use_tagged_queuing = !!ints[5]; } #endif + if (ints[0] >= 6) { + if (ints[6] >= 0) + setup_use_clustering = !!ints[6]; + } } int atari_scsi_reset( Scsi_Cmnd *cmd, unsigned int reset_flags) --------------------- Guenther ----